Download Unit 1 4 Energy, Chemical Reactions and Physical Changes

NAME _______________________________ NOTES: UNIT 1 (4): ENERGY & CHEMICAL REACTIONS
VS. PHYSICAL CHANGES
I)-III) Matter – Sig Figs
IV) Energy: * The ability to create a change or to do work
on Earth, it is described as:
Internal Energy (sum of P.E. and K.E.)
can be divided
The kinetic energy of chemicals
is expressed in the temperature,
and motion of the chemicals
into 2 really big categories
Potential Energy
Kinetic Energy
can be converted to
defined as
defined as
energy of position of
between species relative
to an assumed standard
energy of motion (possessed by
an object in motion)
examples of kinetic energy
examples of potential energy
Chemical
Bond Energy
P.E. is associated with the chemical
energy of bonds.
Electromagnetic Spectrum [Light, Thermal, Microwave];
&then there is/are: Sound energy, motion,
Between bonded species, there is a
bond length or distance and thus the
energy possessed by a chemical is
associated closely with potential
energy … in this case, it’s called,
chemical energy
Now … Let’s break this down … I want to attack the confusion that surrounds key terms like:
work, kinetic energy, potential energy, heat, and temperature.
A) Work: W = (force)(distance)
or
W = (mass)(acceleration) x (distance)
B) Introduction: The Electromagnetic Spectrum …a range/listing of kinetic energies associated with the
movement of electrons. We will see this again, in our work with the atom … but I wish to introduce
it here.
1) Most people do not realize that UV radiation, microwaves, radio waves and visible light
(good ol’ ROYGBV…notice I left out the “I” for indigo) …. are actually variations on the
same theme.
Each is related to the other in that each is a transverse wave which originates, essentially
produced from the movement of electrons, and represents the energy transitions of those e-.
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Spectrum of Electromagnetic Energy
NYS Physics Reference Tables
The wavelength of visible light energy is quite close to the differences in energy experienced by the electrons of bio-chemicals.
Violet:
Indigo:
Blue:
Green:
Yellow:
Orange:
Red:
400 - 420 nm Shortest wavelength of visible light (thus, highest frequency)
420 - 440 nm
440 - 490 nm
490 - 570 nm
570 - 585 nm
585 - 620 nm
620 - 780 nm Longest wavelength of visible light (thus, smallest frequency)
2) There are electromagnetic waves and mechanical waves.
But, first understand, all waves transfer energy, not matter.
Electromagnetic waves can travel through a vacuum … Mechanical waves require a
medium (a system of interacting particles) Mechanical waves may be longitudinal (so called
because they are propagated in parallel with the disturbance e.g. p-waves & sound waves)
and transverse waves.
“When a wave is present in a medium (that is, when there is a disturbance moving through a medium),
the individual particles of the medium are only temporarily displaced from their rest position. There is
always a force acting upon the particles that restores them to their original position.”
http://www.physicsclassroom.com/Class/waves/u10l1b.cfm
a) Sound Waves are mechanical and are longitudinal waves.
http://www.physicsclassroom.com/class/waves/u10l1c.cfm
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Check out: http://www.acs.psu.edu/drussell/demos/waves/wavemotion.html
for an animation comparing mechanical longitudinal and transverse waves
3) We will concern ourselves with the transverse waves, of electromagnetic energy.
These do not require a medium … hence, light, microwaves, radio waves are each
transverse (note, sound waves and radio waves are NOT the same)
http://cse.ssl.berkeley.edu/lessons/indiv/nellie/em_wave.html
Take Home Message: All light waves carry energy. The number of waves per second (Hertz)
is the frequency (related to radio stations…). A higher frequency
is related to a greater the amount of energy per second, transferred.
The electromagnetic transverse wave exhibits two types of fields …
http://www.one-school.net/Malaysia/UniversityandCollege/SPM/revisioncard/physics/wave/electromagnetic.html
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Take Home Message: As an electron moves through “space”, it creates a magnetic field,
which will become important in chemistry …
4) Photonic Radiation refers to energy which is emitted and/or travels in the form of
waves &/or particles called photons
Please understand that light is a form of radiation. Most people think of radiation as nuclear radiation only.
For the most part, the only type of electromagnetic radiation that dovetails with nuclear radiation is limited
to gamma radiation.
…. Okay, now let’s begin to connect this up … with a conversation on…
C) POtential Energy = Energy of * POsition
POtential Energy is essentially due to a POsition of objects: It is the
energy (ability to do work) possessed by an object, due to its position
relative to some standard (assumed) second position. (MR #2)
Vs.
solid phase
(or distance between objects, if you wish...)
gas phase
This is intimately linked to changes in chemical bond energies, phase
changes, the production of light, and intermolecular forces of
attraction(s)
This applies to bond theory, because as a bond is made, the POsition
between the atoms, that will bond, must decrease (they must get closer
to each other). This “getting closer” must occur, if the positive nuclear
forces of one atom are to attract the electron(s) of the other atom. The
LCME gives us the understanding that as this POsition (POtential)
decreases, the energy must go somewhere. Often it is converted into a
form of kinetic energy & is released from the chemicals to the
environment.
Try a bow and arrow as a metaphor…some neat connections are about to be made!
http://clipart.usscouts.org/library/BSA_Cub_Scouts/Cartoons
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Vs.
gravitational potential energy = (m)(gconstant)(height)
GIMME ANother METAPHOR!!!!
How about trying to connect this major reason with .......NASCAR!
http://rubbingsracing.com/rubbingsracingWP/2010/12/15/harraka-prepares-to-head-west-for-showdown/
http://www.marctimesracingnews.com/articles-archive/series-news/1093-nascar-reports/639-nascar-and-its-fans
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D) Often I encourage students to approach chemical bond energy along the line of POsition (as in, there
is a positional distance between species, which changes as atoms bond, or break away from each
other). And while this concept does not work at every point, regarding bonding …it works pretty
darn well … For instance, as expressed by Wikipedia & Dr. Rod Nave at Georgia State’s
Hyperphysics site:
Chemical potential energy is a form of potential energy related to the structural
arrangement of atoms or molecules. This arrangement may be the result of chemical bonds
within a molecule or otherwise. http://en.wikipedia.org/wiki/Chemical_energy
In the chemical bonds of a molecule the attractive electrical forces cause bound states to
exist.
That is, the atoms of the molecule cannot escape the molecule (break away from each other)
without a supply of external energy.
Bound states imply a negative potential energy (a loss of energy) compared to the free
atoms, so any chemical bond has associated with it a negative (loss of) potential energy.
http://hyperphysics.phy-astr.gsu.edu/hbase/molecule/boneng.html
Take Home Message: Making New Bonds releases energy (it is an exothermic process) … As
two free atoms approach each other, position between them clearly decreases, which is
linked to a loss in potential energy … This decrease is “lost” by the reacting chemicals,
to the surrounding environment often, by a conversion of the net change in potential
energy to a form of electromagnetic radiation, such as thermal energy or light
Identify two key ideas from the above passage, which surprise you / inform you / or cause you to
question.
_______________________________________________________________________________
_______________________________________________________________________________
__________________________________________________________________________________________________________
__________________________________________________________________________________________________________
E) Review: Law of the Conservation of Matter and Energy: Matter and Energy can NOT be created nor
(MR #1
links to
MR #2)
destroyed by ordinary chemical means …BUT, energy can be converted into various
forms of energy and/or energy can be transferred.
1) As the potential energy between objects decreases, * it cannot just disappear
potential energy is often converted into some form of kinetic energy (light, thermal, etc…)
And this brings up the nature of a flame… From where, exactly does the energy come?
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F) Kinetic Energy: The ability to create a change or to do work, due to motion (Energy of motion)
1) Generally, the examples of energy with which we are familiar are forms of K.E (each due
to the "motion" or change in position of particles … light, radio waves, thermal
energy… )
2) When particles collide the K.E. can be transferred (as in billiards…)
3) Unit for Energy: joules (J) and kilojoules (kJ)
http://commons.wikimedia.org/wiki/File:Billard.JPG
a) Conversion factor: 1,000 Joules = 1 kJ
Convert: 250.9 kJ = * 250,900
Joules
Convert: 309.4 J =
kJ
* 0.3094
4) Heat: (Latin: calor) Heat is effectively the physical equivalent of work. James Prescott Joule
demonstrated that mechanical work, electrical work, and chemical work each produces a
transfer of energy (heat). In Joule’s words: “The amount of heat (the transfer of energy)
produced by friction is proportional to the work done and independent (regardless) of the
nature of the rubbing surfaces”(The Extraordinary Chemistry of Ordinary Things Snyder 4th ed. p 179) & http://en.wikipedia.org/wiki/Infrared
What most of us don’t get readily is that we need to deal with the Second Law of
Thermodynamics, which has 2 major ideas wrapped up in it.
a) Idea 1: It is impossible to extract all of the energy of a system for work. Some is
irrevocably transferred from the chemicals as heat. That is, when energy is
transferred, there will be less energy available at the end of the transfer
process than at the beginning.
translation:
There is no such thing as 100% conversion of chemical energy into
useable energy (work).
implication:
We can’t win… In every reaction energy is conserved (First Law
of Thermodynamics) … but some of that energy is heat.
As we burn fossil fuels, some of that converted chemical energy is
heat, and essentially transferred to a different system and lost to
us as “useable” work energy …
This is because:
b) Idea 2: Energy flows away from its source, naturally, thus, energy cannot flow from a
colder body to a hotter body, without the addition of even more energy.
translation:
The universe is constantly losing usable energy and never gaining.
We can force the reverse of the natural flow of energy …but that
means we must use up even more energy to do it.
implication:
A working refrigerator won’t keep working, unless plugged in!
Energy won’t flow from cold to warm, spontaneously
c) Conclusion: We age.
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Thus, heat is the sibling of work, and heat is often referred to as a form of energy (but
“heat” per se, is not on the electrochemical spectrum [infrared energy is … but not, heat]
Heat really is equivalent to the amount of energy that is transferred between the reacting
chemicals and surroundings.
This reinforces the idea that heat is the transfer of an amount of energy between two
areas of different energy content. The transfer is from HIGH to LOW (source to sink).
I think the confusion evolves, because in chemistry we are always measuring the heat
transfer and calling it energy (as in exothermic & endothermic reactions). Essentially we do
that, because the measurements are made so that the “work” portion is limited to
virtually zero …encouraging all released energy to be found in the transfer (heat).
Chemists limit the work produced during a chemical reaction, by measuring the
progression of the reaction in rigid, non-flexible containers (a calorimeter). This
limits the work by limiting the movement of the container atoms, over a distance.
[Think about when I pushed against the teacher’s station and it didn’t move, a rigid system]
So, in our measurements (calorimetry) we tend to refer to the energy release only as heat …
(which represents the change in internal energy) …and this is at the heart of the confusion.
Intrinsically we recognize that “heat” is a transfer (a verb) not a specific type of energy.
e.g. We need to "heat up" a cup of coffee. It’s really heating up out here”.
And, some experts don’t even like talking about it as a verb. See: http://hyperphysics.phy
astr.gsu.edu/hbase/thermo/heat.html …. According to the late Dr. Mark Zemansky:
Don't refer to the "heat in a body", or say "this object has twice as much heat as that
body". The First Law of Thermodynamics identifies both heat and work as methods of
energy transfer which can bring about a change in the internal energy of a system.
After that, neither the words work or heat have any usefulness in describing the final
state of the system - we can speak only of the internal energy of the system.
Okay, be aware, that released energy has 2 parts [work and heat], but we, as chemists tend to
focus on the exchange or transfer of energy [the heat, the change in internal energy]. This
exchange is often what we list in a chemical reaction (as in exothermic / endothermic), with a
unit of Joules (J) or kilojoules (kJ).
b) the transfer occurs naturally from areas of * high
energy to areas of
* relatively lower energy or from source to sink: hot to colder
c) And while we’re at it…there is no such thing as cold energy
i) So what can you say to someone when they walk into the
chemistry lab and ask: “Why is this room so cold?”
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Now, listen to me very carefully …. There is another term that confuses us & it too is
not really a form of energy (it’s not on the EMS!!)
4) Temperature
 Energy
(Temperature is a measurement, not a type of energy)
a) When I say, temperature, you think: * measure of average kinetic energy (& vice versa)
i) Think about the idea that temperature  heat nor internal energy
What is/are the unit(s) for measurements of temperature? * K , °C
What is the unit for the measurement of energy, in our course? *joules
Conclusion? _______________________________________________
b) Which has a higher temperature
1 gram of iron at 200°C or 1,000 grams of iron at 200°C?
Which has a greater amount of energy?
This is a bit tricky … We commonly mix up terms like: Temperature, Thermal Energy and Heat…
"Temperature reflects the average total kinetic energy of particles in matter. Or, we could look at
temperature as: “a measure of the ability of a substance, or more generally of any physical system, to
transfer heat energy to another physical system. The higher the temperature of an object is, the greater
the tendency of that object to transfer heat. The lower the temperature of an object is, the greater the
tendency of that object to be on the receiving end of the heat transfer.” http://www.physicsclassroom.com/class/thermalP/u18l1d.cfm
Heat is the transfer of thermal energy; it flows from regions of high temperature to regions of low temperature.
Thermal energy is stored as kinetic energy in the random modes of translation in monatomic substances, and
translations and rotations of polyatomic molecules in gases. Additionally, some thermal energy may be stored as
the potential energy associated with higher-energy-modes of vibration, whenever they occur in interatomic bonds
in any substance. Translation, rotation, and the two types of energy in vibration (kinetic and potential) represent
the degrees of freedom of motion which classically contribute to the heat capacity of a thermodynamic system."
http://en.wikipedia.org/wiki/Heat_capacity
Think About It: When you feel a "draft" in your house, which starts the process?
cold air moving into the house, or warm air moving out of the house?
* Most probably it is do to warm air moving out of the house, first, then being replaced by cold
air moving into the house. This is most likely due to the rising of warm air, and its lost through
a roof, or cooling up against uninsulated walls or windows.
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TRY THIS!
1) A 50.0 gram block of copper at 10ºC is carefully
lowered into 100.0 grams of water at 90.0ºC in an
insulated container. Which statement describes
the transfer of energy in this system?
6) A person with a body temperature of 37 ºC holds
an ice cube with a temperature of -5.0 ºC in a room
where the air temperature is 20 ºC. The direction of
heat flow is from the:
(1) The water loses heat to the block until
both are at 10.0ºC.
(1) person to the ice, only
(2) person to the ice and air and from the air to the ice
(2) The block gains heat from the water until
both are at 90.0 ºC.
(3) ice to the person, only
(3) The water loses heat and the block gains
heat until both are at the same temperature
that is between 10.0 ºC and 90.0 ºC.
(4) ice to the person and air, and from the air to the
person
7) A cold pack is placed on an injured leg.
(4) The water gains heat and the block loses
energy until both are at the same temperature
which should be between 10.0 ºC & 90.0 ºC.
a) Indicate the direction of the flow of energy
between the leg and the cold pack ____________
_______________________________________
2) The average kinetic energy of water molecules is
greatest in which of these samples?
STOP! Any key
(1) 10 g of water at 35ºC
(2) 10 g of water at 278 K
(3) 100 g of water at 288 K
(4) 100 g of water at 45 ºC
terms you
should
interpret???
Energy should apply to the energy exchange
that occurs between the cold pack and injured
leg (edited June ‘02).
3) Two samples of gold that have different
temperatures are placed in contact with one
another. Energy will flow spontaneously from
a sample of gold at 60°C to a sample of gold
that has a temperature of
(1) 50°C
(2) 60°C
b) Describe how the Law of Conservation of
8) Using the concepts of potential energy, explain how a
gas becoming a liquid, releases energy. You can write
or use (a) diagram(s)
(3) 70°C
(4) 80°C
4) An iron bar at 325 K is placed in a sample of water
The iron bar gains energy from the water when the
temperature of the water is
(1) 65 K
(2) 45 K
(3) 65°C
(4) 45°C
5) Which term represents some form of energy?
(1) heat
(2) degree
(3) kilojoule
(4) temperature
9) As the temperature of a gas increases from 0°C
to 10°C at constant pressure, the volume of the gas
will
(1) decrease by 1/273
(2) decrease by 10/273
selected answers:
1) 3 2) 4 3) 1
4) 3
5) 3
(3) increase by 1/273
(4) increase by 10/273
6) 2 ...... 9) 4
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How can a poor first year student tell the difference
between a chemical reaction and a physical change?
V)
CHEMICAL REACTIONS
(involve breaking AND making new bonds
&/or involving changes in the e- clouds)
reduce / reduction
oxidize / oxidation
combust / burn / flammable
rust / corrode
react / bond
ionize / ionized
neutralize
decompose
cook / grill
synthesize
precipitate
flash point
polymerize
change in oxidation state
versus
Physical Changes / Properties
(May involve breaking bonds, but no new bonds are made
Physical changes may occur with chemical reactions)
dissolve / stir (so as to make an aqueous solution)
mix / mixture
melt / fuse
vaporize / boil / evaporate
sublime or sublimate
distill
freeze
condense
filter / separate
density (when calculating, comparing samples)
measuring / comparing masses
measuring / comparing volumes
color
liquefied, solidified, (change in phase)
smell
NOT EVERYTHING THAT HAPPENS IS A CHEMICAL REACTION, but many
chemical reactions may involve a physical change in the matter. eg. forming an (aq) and a new solid...
2 ways to determine when a chemical reaction has occurred
On A Test
In Your Life
When there’s a re-arrangement of
at least 2 of the 5 visual cues
element symbols so that new
when there is a bold color change
(not pre-existing) substances are produced.
when a new solid (precipitate) is produced
when a new gas is produced (fizzing, bubbles)
when a new liquid is produced (hard to tell when this happens)
when energy is absorbed or released (found in most interactions)
TAKE HOME MESSAGE: Bond Breaking (alone) does NOT mean a chemical reaction has occurred.
In reality a chemical reaction occurs only when * new bonds are made (When bonds are just broken ...
it is not a chemical reaction … it could imply melting or dissolving in water, for example). A chemical
property involves the activity (loss / gain or sharing) of electrons.
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VI) Reading a reaction equation
A) Start at the reaction arrow (), which can be thought of as an equals (=) sign
B) Summary of a reaction:
coefficient
subscript
Fe2O3(s) + 2 Al(s)  2 Fe(s) + Al2O3(g) + 4,000 J
Reactants
Products
tells you some sort of change has occurred (equivalent to an = sign)
Note: no subscript or no coefficient means "1"
the “+” sign is not arithmetic, it means the word, AND
1) Chemical Formula: a series of letter symbols representing the elements that comprise a
compound, and the specific ratio between these elements represented by small subscripts
a) Subscript: Applies only to the element(s) it “modifies” …
inside ( )
next to
Na2S
Ca3(PO4)2
b) Coefficient: Used to represent the amount of the chemical (formula) … it applies
to the entire substance
2) Often, energy (kJ or J) is included on one side or another of the reaction.
a) If:
* reactant(s)

product(s) and kJ
i) vocabulary word: *exothermic (energy is released, and is on the product side)
ii) Meaning: the chemicals release to the environment more energy due to
new bonding, than is gained to break bonds. The environment
(water in a beaker or the air of the room) gets hotter.
b) If:
* kJ + reactant(s)  products
Students do not always
know how to classify a
cooling cup of coffee.
In terms of exothermic
and endothermic ... how
would you classify the
process?
i) vocabulary word: *endothermic (energy is on the reactant side)
ii) Meaning: more energy is absorbed by the reacting chemicals to break the
bonds, than is released to the environment as new ones are made.
* The environment (the water in a beaker of the air) * supplies
the energy and thus the environment becomes cooler.
Think About This: When trying to classify a process in lab, as exothermic or endothermic, watch how the temperature of the
surroundings changes. An exothermic process releases energy, causing the temperature of the surroundings (air / water) to rise.
The chemicals of an endothermic process absorb energy from the environment and the temperature of the surroundings drops.
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On Problem Solving / Discovery Learning and Exothermic Reactions:
A Historical Sidelight: Ira Remsen on Copper and Nitric Acid
Ira Remsen (1846-1927) founded the chemistry department at Johns Hopkins University, and founded one of the first centers for
chemical research in the United States; saccharin was discovered in his research lab in 1879. Like many chemists, he had a vivid
"learning experience," which led to a heightened interest in laboratory work:
While reading a textbook of chemistry I came upon the statement, "nitric acid acts upon copper." I was getting
tired of reading such absurd stuff and I was determined to see what this meant. Copper was more or less
familiar to me, for copper cents were then in use. I had seen a bottle marked nitric acid on a table in the doctor's
office where I was then "doing time." I did not know its peculiarities, but the spirit of adventure was upon me.
Having nitric acid and copper, I had only to learn what the words "act upon" meant. The statement "nitric acid
acts upon copper" would be something more than mere words. All was still. In the interest of knowledge I was
even willing to sacrifice one of the few copper cents then in my possession. I put one of them on the table,
opened the glass vial marked nitric acid, poured some of the liquid on the copper and prepared to make an
observation. But what was this wonderful thing which I beheld?
The cent was already changed and it was no small change either. A green-blue liquid foamed and fumed over
the cent and over the table. The air in the neighborhood of the performance became colored dark red. A great
colored cloud arose. This was disagreeable and suffocating. How should I stop this? I tried to get rid of the
objectionable mess by picking it up and throwing it out of the window. I learned another fact. Nitric acid not
only acts upon copper, but it acts upon fingers. The pain led to another unpremeditated experiment. I drew my
fingers across my trousers and another fact was discovered. Nitric acid acts upon trousers. Taking everything
into consideration, that was the most impressive experiment and relatively probably the most costly experiment
I have ever performed. . . . It was a revelation to me. It resulted in a desire on my part to learn more about that
remarkable kind of action. Plainly, the only way to learn about it was to see its results, to experiment, to work in
a laboratory.
from F. H. Getman, "The Life of Ira Remsen"; Journal of Chemical Education: Easton, Pennsylvania, 1940; pp 9-10; quoted in Richard W. Ramette,
"Exocharmic Reactions" in Bassam Z. Shakhashiri, Chemical Demonstrations: A Handbook for Teachers of Chemistry, Volume 1. Madison: The
University of Wisconsin Press, 1983, p. xiv:
1) Write the names of the reactants involved in Remsen’s first experiment. * nitric acid + copper
2) Identify 2 physical characteristics of the products of that chemical reaction. *green-blue color, gas, liquid odor
3) Will nitric acid react with cotton? * yes
Defend your answer by citing the reading: * his trousers reacted
4) Will nitric acid react with glass? * No Defend your answer by citing the reading: * It was kept in a bottle.
5) Will nitric acid chemically react with skin? * Yes
6) What might you infer about the composition of cotton and skin? *They have a similar composition
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TRY THIS! …Remember, the loss or gain of energy is from the “point of view” of the
chemicals … When chemical systems lose energy, the environment (water or air) becomes
warmer. When chemical systems gain energy, the environment (water or air) supplies the
energy gained by the chemicals, and thus the environment becomes cooler in temperature.
___1.
I am providing you with "before and after" diagrams for this question. Analyze them to see if they help you.
A student took the temperature of 150.0 mL of water. She then dissolved 5.00 grams of NH4Cl(s) into
the water according to the equation
H2O(𝓁)
NH4Cl(s) + 14.7 kJ 
just 150 mL water
NH4+1(aq) + Cl-1(aq)
150 mL of water plus
the dissolving NH4Cl
http://www.wpclipart.com/science/beaker/beaker.jpg
THINK!
Is this dissolving process, endothermic or exothermic?
Is the chemical NH4Cl absorbing energy from the water, OR releasing energy into the water, as NH4Cl dissolves?
If the chemical were absorbing energy from the water, what should happen to the temperature of the water?
If the chemical were releasing energy to the water, what should happen to the temperature of the water?
She took the temperature of the resulting solution. Using the above equation and her knowledge of
thermal energy, she could predict that the dissolving process was:
a)
b)
c)
d)
___2
endothermic & the temperature of the water increased
endothermic & the temperature of the water decreased
exothermic & the temperature of the water increased
exothermic & the temperature of the water decreased
Given the reaction: A(s) + B(aq)  C(s) + D(aq) + 170 kJ
Assuming that the reaction occurs in water, as the reaction ends, the temperature of the resulting solution
have:
a) increased
b) decreased
c) remained the same
Think: Is this chemical reaction endothermic or exothermic?
Are the chemicals, as they react, absorbing energy from the environment or are
the chemicals, as they react, releasing energy into the environment?
If the chemicals were absorbing energy, what should happen to the temperature of the water?
If the chemicals were releasing energy, what should happen to the temperature of the water?
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For questions 3 - 5 use the following choices. A choice may be used once, more than once or not at all.
a) endothermic
b) exothermic
52.4 kJ + 2 C(g) + 2 H2(g)  C2H4(g)
___3)
H2O
___4)
NaOH(s)  Na+1(aq) + OH-1(aq) + 44.3 kJ
___5)
2 HCl(aq) + Fe(s)  FeCl2(aq) + H2(g) + 598 kJ
___6) A student took the temperature of 150.0 mL of water. She then dissolved 30.00 grams of KClO3(s) into
the water according to the equation:
H2O (𝓁)
KClO3(s) + 41 kJ
 K+1(aq) + ClO3-1(aq)
She took the temperature of the resulting aqueous solution. Using the above information and her
knowledge of chemistry she could infer that the reaction was :
a)
b)
c)
d)
endothermic
exothermic
exothermic
endothermic
&
&
&
&
the temperature of the surrounding water increased
the temperature of the surround water increased
the temperature of the surrounding water decreased
the temperature of the surrounding water decreased
7) Imagine that you and a friend are sitting in front of a wood fire. The reacting chemicals in this case, are the
orgainic gases of wood and dioxygen (O2(g)) gas from the air. Is the reaction exothermic or endothermic?
Wood + O2  CO2(g) + H2O(g)
8) Consider liquid water freezing into solid water-ice. Is this exothermic or endothermic?
H2O(𝓁)  H2O(s)
9) What confuses you or what do you think you now know? ______________________________________
__________________________________________________________________________________
Ans:
1) b energy is absorbed by the reactants. the source of energy is most probably from the water, thus energy would move from the water to the
chemicals, and the temperature of the resulting solution would be lower than the water's temperature.
2) a it is an exothermic reaction (energy is on the product side) ... the chemicals release more energy than absorbed and thus the water gains that
energy.
3) a 4) b 5) b 6) d
7) exothermic ... energy is being released from the reacting chemicals ... far more than was added to get the fire going...
8) exothermic ... this is a cooling process and yes, also exothermic ... the chemical (water) must lose energy to the environment...
120
VI) Put It All Together:
A Recall: A chemical reaction has at least 2 of the following 5 observable changes.
1) thermal energy or light is released / absorbed
2) a new substance is produced:
a new solid (s), or precipitate is produced (easily seen)
Ba(NO3)2(aq) + Na2SO4(aq) 
2 NaNO3(aq) + BaSO4(s) this is a bright white solid
that settles out of solution
a new gas (g) or bubbling/fizzing is produced (easily seen)
Zn(s) + 2HCl(aq) 
H2(g)
+
ZnCl2(aq)
bubbles out of solution
l
a new liquid ( ) is produced NOT (aq) (hard to identify this one visually, so it is not used, often)
3) there is a bold color change Pb(NO3)2(aq) + 2 KI(aq)  PbI2(s)  +
colorless
colorless
2 KNO3(aq)
bright yellow precipitate colorless
4) A simple physical change generally has only 1 of the aforementioned changes
a) Note: Ice melting to water … is NOT creating a new liquid (substance)
H2O(s) + 334 kJ → H2O(l)
Note: Soda pop fizzing (releasing the trapped CO2(g) is NOT creating a new gas …
The CO2(g) is already present in the soda...it is just now escaping.)
PRACTICE: Use the reasoning of the re-arrangement (new bond making), of atoms / ions or lack thereof, to
identify each of the following as a chemical reaction or physical change.
1) Identify the following as being a physical change or a chemical reaction and then defend your answer using
the concept of new bond formation (or the lack thereof).
very often, water breaks or disrupts the ionic bond
Al3+(aq) + 3 Cl-1(aq)
really the new bonds are in H2
2 Al(s) + 6 HCl(aq)  2 AlCl3(aq) + 3H2(g) + 134 kJ
This represents a _____________________________ because_______________________________
_________________________________________________________________________________
2) Identify the following as being a physical change or a chemical reaction and then defend your reasoning.
Be sure your defense uses a “because” statement which quotes the theory studied in class.
Fe(s) + CuSO4(aq)  Cu(s) + FeSO4(aq) + 30 kJ
This represents a _____________________________ because_______________________________
_________________________________________________________________________________
121
3) Identify the following as being a physical change or a chemical reaction and then defend your reasoning.
Be sure your defense uses a “because” statement which quotes the theory studied in class.
H2O(l)
50 kJ + NaCl(s) 
or:
Na+1(aq) + Cl-1(aq)
H2O(l)
50 kJ + NaCl(s)  NaCl(l)
This represents a _____________________________ because_______________________________
_________________________________________________________________________________
4) Identify the following as being a physical change or a chemical reaction and then defend your reasoning.
Be sure your defense uses a “because” statement which quotes the theory studied in class.
100 kJ + CH3OH(l)
 CH3OH(g)
This represents a _____________________________ because_______________________________
_________________________________________________________________________________
5) Identify the following as being a physical change or a chemical reaction and then defend your reasoning.
Be sure your defense uses a “because” statement which quotes the theory studied in class.
2 Al(s) + 3 I2(s)  2 AlI3(s) + 80kJ
This represents a _____________________________ because_______________________________
_________________________________________________________________________________
For questions 6 -15 use the underlined boldfaced verb as your clue. Let me know if you think the situation
describes a chemical reaction / property or a physical change or property.
6) ____________________ Pat dissolved 10.0 grams of NaOH(s) in water.
7) ____________________ Jordan quickly grilled the steak for every late guest.
8) ____________________ Terry melted the butter and flour together to create a rue for the sauce
9) ____________________ Taylor saw that the metal door handle had oxidized and it needed to be replaced
10) ___________________ Alex was careful to distill the solution to isolate a sample of pure water.
11) ___________________ Perry used baking soda to neutralize the tomato sauce making the taste less tangy
12) ___________________ Sam shredded all the documents listing a social security number.
13) ___________________ Ryan burned the marshmallows in the campfire.
14) ____________________Sidney determined the melting point of the solid to be 58.3C
15) ___________________Shaun noted that a can of Coke was denser than Diet Coke, in water
16) ___________________Aidan filtered the coffee, using unbleached, paper filters.
122
VII) States of Matter (solid, liquid, gas) and the Kinetic Molecular Theory of Gases
A) State or Phase: a property of matter, based upon the arrangement and/or “spacing” between the
the species. The phase of a substance is dependent upon pressure and temperature, for these two
factors affect the attractive forces between species, and thus the arrangement of those species.
The term, “state” of matter is generally referred to as solid, liquid or gas.
1) Solid Phase: Classically, true solids are classified as *crystals or as crystalline, exhibiting a
repeating lattice structure (a specific geometry building the matter), with a fairly specific melting point
From: http://shell.cas.usf.edu/~mccolm/research/RetGeometry.html
The reticular (net-like) repeating structure of a fullerene
or:
http://www.diamondstamps.eu/res/Default/clip_image005.jpg
A generalized view of the structure of a diamond.
a) the species of making the matter in the solid phase, vibrate in position
b) Crystals & powders are examples of matter in the solid phase.
i) many students become confused with powders, because they can “be poured”
but they are definitely classified as a solid!
ii) Macromolecules like diamond & quartz are also solids
c) Over recent decades the concept of amorphous solid has developed. These are
“hard”, but not classically classified as “true solids” … These are solids but they
lack an extended geometric lattice pattern.
i) plastics, rubber, wax, and glass are often classified as amorphous solids.
d) Regardless of the classification, solids have a fixed volume (it does not change when
moved from one beaker to another of a different size, for example)
e) by definition … solids are * frozen!!!!
2) Fluid Phases: BOTH the Liquid and Gaseous phases are described as fluids.
a) Liquid Phase: The “melted” phase of matter … Liquids have a relatively constant
volume, yet the species are separated from each other, sufficiently to allow a “flow”
or movement around and over each other.
b) Gaseous Phase: The vaporized form of matter, in which the distance between the
species is maximized, & the arrangement of the species is at its most random.
123
B) Phase Changes are physical changes. …. No new bonds are made.
It requires energy to change from solid to liquid to gas (endothermic)
Energy is released to the environment (exothermic) as matter cools
from gas to liquid to solid
C) Heating (and/or Cooling Curves) and Calorimetry
http://en.wikipedia.org/wiki/Supercritical_fluid
vaporization
1) We can use q = mcΔT whenever there is a *change in temperature
a) ΔT = Tfinal – Tinitial
b) 100.0 grams of water were heated from 35.0°C to 55.0°C, calculate the energy
absorbed by the water.
2) We can use q = mHf when a sample is *melting … where Hf is a constant giving the
number of Joules required per gram to melt at a constant temperature
3) We can use q = mHv when a sample is * boiling or vaporizing at a constant temperature
4) See Table C of your reference charts for constants
124
VIII) Applying Energy: Calorimetry: The measurement of the thermal energy (Joules) contained by chemicals.
By using calorimetry calculations, we can determine the change in enthalpy (q or ∆H) of a
chemical reaction or of a physical change.
This is important for most chemical reactions but also for many engineering issues, such as the
integrity of metals used to make pots and pans to the ceramic heat tiles (heat shield) designed to
protect the Space Shuttle on re-entry.
There are three DIFFERENT calorimetric calculations.
Equation
q = mHf
Key Words and / or Clues
melting / freezing / solid  liquid
q = mHv
boiled / vaporized/ condensed /
liquid  gas
change in temperature
q = mc∆T
Requirements
Use the equation & constant for "Hf"
Use the equation & constant for "Hv"
Use the equation & constant for "c"
Calling all Historians and Engineers! According to the Science Channel's 2008 Moon Machines:
Lunar Rover, each metal mesh wheel of the first rover, was run by its own electric motor, powered by its
own battery system. Fear of becoming too cold or too hot and a maximum 10 lbs. weight limit for the
cooling system for the batteries had engineers getting creative. They used a series of cells, containing
paraffin (wax!), which, as the batteries released energy, could absorb the released energy and melt, yet
maintain a relatively constant temperature, of the system while in use. When not in operation, a series of
radiator panels were raised, allowing the paraffin to solidify in the cold of space, becoming ready for the
next use of the rover....!!!!!
To quote a Kellogg’s® Pop Tart commercial…. That is so “cool”… It’s “hot”… So “hot”, it’s “cool”
1) The reading suggests that as batteries “work” or are used, energy is released. Given all of our work regarding
reactions and bonding to date … What must be happening in the battery, that results in released energy?
*new bonds (of more stable products) are being produced …. bond production releases energy
&/or a chemical reaction is occurring, in which work and heat [the definition of released energy]
125
A) Calorimetry problems: when the temperature changes.
1) The changes in chemical energy can’t be determined directly (…like using a machine for a
measurement) … But we can use the change in temperature between unequal matter, to
determine the change in energy (q or ∆H) ….
This idea gets us back to measuring “heat” by limiting the work.
2) q = mc∆T
Key ideas : Joules and a temperature change
Where: q = Joules (J) or the heat exchange / change in enthalpy
m = grams or the mass of material
ΔT = K or ºC which is the change in temperature
c = J or J g-1 K-1 specific heat (a different constant for each substance &
g•K
phase of the substance)
3) Calorimeter: An instrument which helps to measure the q of a substance by allowing a
known mass of water to absorb its energy.
Fact1: We can’t get the temperature change
of a burning substance directly
Fact2: The environment surrounding a burning
object absorbs the released energy
Fact3: Due to its construction (e.g. stainless steel)
no work is done on the calorimeter. Thus, we
can assume that the joules absorbed by the
surroundings = the joules released by a
burning substance, en toto.
Fact4: Using
mwatercwaterTwater
NOW, we
http://tinyurl.com/l2ugtu8
can now calculate the qwater absorbed
Fact5: qwater absorbed = the qreleased by the burning sugar
126
3) A little about specific heat:
a) every substance has a different specific heat …. even the specific heat of the phases of
each substance can be different values.
e.g.) H2O(l) = 4.18 J g-1 K-1
& H2O(s) = 2.03 J g-1 K-1
b) specific heat (c) = the # of joules required to change the temperature of 1.00 g of
substance by 1.0 K (or change it by 1.0 ºC) … it is an intensive property
i) There is a general rule about specific heat and changes in temperature, the
greater the specific heat, the slower temperature change occurs.
★★Hence: Slow to heat up, Slow to cool down.
ii)
Check out:
http://tinyurl.com/l2ugtu8 for more on specific heat and calorimetry
The high specific heat of liquid water has important implications for life on Earth. A given mass of
water releases more than five times as much heat for a 1°C temperature change as does the same
mass of limestone or granite. Consequently, coastal regions of our planet tend to have less variable
climates than regions in the center of a continent. After absorbing large amounts of thermal energy
from the sun in summer, the water slowly releases the energy during the winter, thus keeping coastal
areas warmer than otherwise would be expected (see the diagram below). Water’s capacity to
absorb large amounts of energy without undergoing a large increase in temperature also explains
why swimming pools and waterbeds are usually heated. Heat must be applied to raise the
temperature of the water to a comfortable level for swimming or sleeping and to maintain that level
as heat is exchanged with the surroundings. Moreover, because the human body is about 70% water
by mass, a great deal of energy is required to change its temperature by even 1°C. Consequently, the
mechanism for maintaining our body temperature at about 37°C does not have to be as finely tuned
as would be necessary if our bodies were primarily composed of a substance with a lower specific
heat.
Title: The High Specific Heat of Liquid Water Has Major Effects on Climate
Regions that are near very large
bodies of water, such as oceans or
lakes, tend to have smaller
temperature differences between
summer and winter months than
regions in the center of a continent.
The contours on this map show the
difference between January and July
monthly mean surface temperatures
(in degrees Celsius).
******************************************************
127
Selected Examples of Specific Heat Values
Substance or Mixture
Water (liquid)
Water (gaseous)
Aluminum
Ethanol
Iron
Lead
Mercury
Gold
Diamond (C(s))
Graphite (C(s))
Silicon Dioxide (quartz)
Calcium Carbonate
Ammonia (liquid)
Specific Heat
(J/g∙K)
4.18
2.06
0.895
2.4
0.46
0.130
0.14
0.129
0.509
0.709
0.742
0.915
4.7
Check out the specific heat values for
liquid water, water vapor (gaseous
water). Can you suggest a reason for
what you observe?
Check out the value for liquid ammonia
(NH3(𝓁) What’s up with that?
QUESTIONS: For questions 1-5 use the table of specific heat values.
1) Which sample would increase in temperature faster? Explain your answer. (Be sure to have a “because
statement” in your answer. This “because statement” should include a quote from notes, a reading, a metaphor or an equation.)
20 grams of ethanol (alcohol) or 20 grams of water?
________________________________________________________________________________
________________________________________________________________________________
_________________________________________________________________________________
2) Which would make a more sensitive fluid for a thermometer: Mercury or Ethanol? ______________
3) A saucepan is often made of stainless steel, which is an alloy made primarily of iron. When you
put a pan full of water on the stove which heats up faster, the pan or the water in the pan?
_______________Defend your answer (Be sure to have a “because statement” in your answer. This statement should
include a quote from notes, a reading, a metaphor or an equation.)
Why? ____________________________________________________________
__________________________________________________________________
Answers: 1) 20 grams of ethanol will heat up faster because ethanol has a lower specific heat of 2.4 J/g K, compared to water’s 4.18 J/g K. This means that every
gram of ethanol requires only 2.4 J of absorbed energy to increase it’s temperature. Since it requires a lesser amount of energy, it will heat up faster.
2) Mercury. 3) The pan. The pan is mostly iron, so the specific heat is roughly close to 0.46 J/g K. The specific heat of water is 4.18 J/g K. The metal
pan will heat up faster than the water, since it requires less energy per gram to change temperature (has a lower specific heat value).
Keep going…
128
4) You are camping and you wrap up some fish in aluminum foil and cook it over a campfire. (As with
most vertebrates, it has a lot of water) After 8 minutes or so, the foil-wrapped fish is taken off the fire. One
minute later, the aluminum foil is basically cool enough to touch so you can unwrap your dinner ...
but the fish is still hot. (Be sure to have a “because statement” in your answer. This statement should include a quote from
notes, a reading, a metaphor or an equation.)
What’s up with that? _____________________________________________________________
_______________________________________________________________________________
__________________________________________________________________________
5) Identify 1 material more sensitive to changes in energy than diamond, but is not as sensitive
as gold. (There are at least 3 on the table of specific heat values)… _________________________
4) Aluminum has a much lower specific heat than water (0.895 J/g K compared to 4.18 J/g K). This means that because it requires less energy per
gram, to change in temperature by 1 K (or °C), the aluminum will cool (change temp) much more quickly than the mostly water containing fish.
5) iron, lead or mercury
************************************************
B) A little bit more about T
1) as written, the T value probably is not one of the listed temperatures, in the
given problem … but rather it is the change or difference between the
final temperature of the matter and the initial temperature.
a) this leads to a second equation: T = Tfinal -Tinitial
Using this equation, you can determine the final temperature of a sample, when
you know the initial temperature and the change in temperature, or some other
variation.
i) you can assume, that when energy is absorbed, then the final temperature will
be greater than the initial, assuming there is no change in phase.
you can assume, that if the system were cooled, then the final temperature will
be less than the initial temperature, assuming there is no change in phase.
ii) Theoretically, the temperatures should be in K, but the change in the Kelvin
temperature = the change in temperature in C.
Huh?? .... Essentially:
∆C = ∆K
Consider the following:
Temperature Scale
Celsius
Kelvin (equivalent)
Tinitial
10C
283K
Tfinal
15C
288K
Difference (∆T)
5C
5K
129
2) Problem: Calculate the energy absorbed in joules when 254.00 grams of water are
heated from 320.0 K to 355.0 K
Equation:
Substitution: * (254.00g) (4.18 J ) (35.0 K)
g•K
Answer: * 37200 J
PRACTICE: Use your understanding of calorimetry to complete each of the following problems. I URGE you
to use E.S.A.. Watch those sig. figs!!
___1) How many joules are absorbed by 50.0 g of water as they are heated from 335.0 K to 355.0 K?
a) 4,180
joules
E:
b) 10.5 joules
S:
6
c) 2.10 X 10 joules
_
d) 2,100 joules
A:
___2) Calulate the change in temperature experienced by 70.00 g of water cooled by the release of
8,820 joules.
E:
a)
b)
c)
d)
40.0 °C
10.6 °C
30.1 °C
50.8 °C
S:
A:
___3) What mass of water was heated when 2.10 x 103 joules were absorbed between the temperatures of
90.0 °C and 95.0°C? (Do you need to convert to Kelvin?)
a) 10. grams
_
b) 100 grams
E:
S:
c) 5.0 grams
d) 72 grams
A:
130
___ 4) Calculate the change in temperature which occurs when 100.0 grams of water are cooled by the
release of 2.1 x 103 joules of heat energy.
_
E:
a) 50 K
c) 5,000 K
b) 5.0 K
d) 1.0 K
S:
A:
___ 5) Calculate the change in enthalpy, in joules, that are absorbed when 75.602 grams of water are heated
from a temperature of 288.0 K to a temperature of 298.0 K.
E:
a) 31.6 joules
b) 15.6 joules
c) 3.16 x 103 joules
S:
d) 1.96 x 104 joules
A:
___6) Calculate the mass, in grams, of water cooled from 100.0°C to 60.0°C assuming a release of
6.720 x 103 joules.
a)
b)
c)
d)
80.1 g
60.0 g
30.7 g
40.2 g
___7) What is the temperature change that results when 6.3 x 104 joules of heat are added to 300.0 g of water?
a)
b)
c)
d)
50. °C
52 °C
48 ° C
10. °C
___8) Calculate the change in enthalpy required to change the temperature of 300.g of water by 40.0°C
a) 5.88 x 104 joules
b) 5.02 x 104 joules
c) 6.30 x 104 joules
d) 7.00 x 104 joules
___9). Challenge Problem 25.000 grams of water at a temperature of 45.0°C absorbed 3,360 joules of
energy. Calculate the FINAL temperature of the water.
a)
b)
c)
d)
45.8
77.2
13.4
89.0
°C
°C
°C
°C
131
___10) Challenge problem 60.000 g of water in a beaker were at a temperature of 35.0C. What would
be the FINAL temperature of the water, were it to absorb 2,016 joules?
a) 8.00 °C
b) 27.0 °C
c) 43.0 °C
d) 103.0 °C
___11) Challenge problem: 248.000 g of water were in a beaker. The water was heated and absorbed
3.1878 x 103 joules. If the final temperature of the water were 95.0 °C calculate the INITIAL
temperature of the water.
a)
2 °C
b) 111.0 °C
12)
c)
d)
3.03 °C
91.9 °C
a) The apple filling of an apple pie is mostly water. By how much will 200 g of
apple filling cool if it loses 8.360 x 103 J of energy?
b) The mixture, of pie crust has a specific heat of 0.836 J/gK.
By how much will 200 g of crust cool if it loses 8.360 x 103 J of energy?
c) When I bite into a heated piece of apple pie, I often burn the roof of my mouth.
I don’t get that. The pie crust was cool to the touch … why do I get burned?
__________________________________________________________________
__________________________________________________________________
Answers : 1) a 2) c 3) b 4) b 5) c 6) d 7) a
8) b
9) b 10) c 11) d 12 a) 10 K or 10°C 12 b) 50 K or 50°C
12c) It has to do with the differences of specific heat. Because the crust’s specific heat is about 5 times lesser than that of water’s, the pie crust will
cool off far more quickly …. slow to heat up, slow to cool down … and vice versa
132
5) Changes in potential and average kinetic energy
vaporization
a) POtential energy = energy of POsition
i) It is the energy associated with chemical bonds
ii) As species move closer to each other, PE decreases
iii) As species move farther away from each other PE increases
iv) question: When something such as wax melts or fuses to liquid, what is
occurring to the potential energy of the molecules of paraffin?
b) Average Kinetic Energy = the *temperature of a chemical system
133
Practice:
1) How many Joules of energy are required to melt 25.0 grams of ice completely
at a constant temperature of 0C? (ans: 8,350 J)
vaporization
a) What is happening to the PE? * increasing
2) 14.0 grams of ice were melted completely at a constant temperature of 0˚C. How many
Joules of energy were required to melt the ice completely at 0C? (ans:4680 J)
vaporization
a) What is happening to the average KE? * remains the same
3) A student melted 50.0 grams of an unknown compound, at a constant temperature of 73.2 C.
She calculated the number of Joules required for the fusion to be 1.34 x 104 J. What is the
heat of fusion constant for this unknown substance ?
vaporization
4) A student vaporized a mass of water at a constant temperature of 100.0C.
If 4.50 x 105 J were absorbed by the water, what was the mass? (ans: 199 grams)
vaporization
134
5) What mass of aluminum solid was completely liquefied at its melting point of at 660.4 C, if
17,800 Joules were absorbed? (For aluminum, Hf = 396.9 J/g) (ans: 44.8 grams of Al)
6) Calculate the Joules of energy released as 45.0 grams of water vapor condensed to
liquid at 100. C (ans: 102,000 J)
7) Calculate the number of Joules absorbed by 50.0 g of water as they are heated from
335.0 K to 355.0 K? (ans : 4,180J)
vaporization
8) What was the change in temperature when 70.00 g of water were cooled by the release of
8,820 Joules? (ans: 30.1 °C)
9)
25.000 grams of water at a temperature of 45.0°C absorbed 3,360 Joules of
energy. Calculate the FINAL temperature of the water. (ans: 77.2 °C)
vaporization
135
10) 60.000 g of water in a beaker were at a temperature of 35.0C What would be the
FINAL temperature of the water, were it to absorb 2,016 Joules? (ans: 43.0 °C)
11) What mass of water was heated when 2.10 x 103 Joules were absorbed between the
temperatures of 90.0 °C and 95.0°C? (ans: 1.0 x 102 grams)
vaporization
12) 248.000 g of water were in a beaker. The water was heated and absorbed 3.1878 x 103 J
of energy. If the final temperature of the water were 95.0 °C, calculate the INITIAL
temperature of the water . (ans: 91.9 °C)
13) Calculate the change in temperature which occurs when 100. grams of water are cooled by
the release of 2.1 x 103 Joules of heat energy. (5.0 K or 5.0°C )
vaporization
a) Why can the answer be in K or in °C?
136
Extra Practice: HEATING / COOLING CURVES AND PHASES
__1) Which graph best represents the change of phase of a substance from a gas to a solid, using the axes of
temperature as a function of time ?
For questions 2 and 3 use the following graph and information: The graph below represents a graph of
temperature as a function of time of as a substance is heated uniformly, starting at a temperature below the
substance's melting point.
___ 2) Which portions of the graph represent times when energy is absorbed and the potential energy increases,
while the average kinetic energy remains constant ?
a) A  B
b) B  C
c) C  D
d) E  F
___3) Between which two time periods are the liquid and the gas phase both present?
a) t0  t2
b) t2  t3
c) t3  t4
d) t4 and beyond
137
For questions 4-6 one or more of the responses given is (are) correct. Using your understanding of chemistry
decide which of the responses is (are) correct. Then choose:
a)
b)
c)
d)
e)
if only I is correct
if only II is correct
if only I and II are correct
if only II and III are correct
if I, II, and III are correct
Questions 4-6 each deal with the following cooling curve of a substance as it uniformly cools from a gas to
below its melting point. Be sure that you refer to this diagram for each question.
___ 4) Given the above cooling curve :
I)
from C to D, the potential energy of the substance decreases
II) from C to D, the average kinetic energy of the substance decreases
III) from E to F, both liquid and the solid phase are present
___ 5) Given the above cooling curve :
I) it is a graph of temperature as a function of time.
II) the melting point of the substance is approximately 60. ˚C
III) the substance is probably water, based on the melting point.
___ 6) Using the above cooling curve, from point B to C,
I) potential energy is decreasing (-∆S)
II) the average kinetic energy is constant
III) the temperature is decreasing
138
___ 7) Which change of phase is exothermic?
a) NaCl(s)  NaCl(𝓁)
c) H2O(𝓁)  H2O(s)
b) CO2(s)  CO2(g)
d) CCl4(𝓁)  CCl4(g)
___ 8) What is the total number of Joules of energy absorbed by 15.0 grams of water when it is
heated from 303.0 K to 313.0 K?
a)
627 J
c) 89.9 J
b)
6,260 J
d) 630.J
___ 9) Given the following heating curve, of a substance as it uniformly heats from a solid below its melting
point to beyond its boiling point, which single choice is most correct ?
a) The melting point of the solid approximately equals 50 ˚C
b) Vaporization occurs at approximately 80 ˚C
c)
It takes more time to melt the substance than it does to boil it away
d)
Only liquid is present between points B and C
F
D
B
E
C
A
139
Special Directions: For questions 10-14 write down the most appropriate equation. You do not need to solve
the following problems. Simply write down the equation you should use were you to solve the problem.
10) Calculate the number of Joules absorbed by 20.00 grams of ice as the ice melts at 0.0˚C.
11) The temperature of 110 g of water rises from 25.0°C to 26.2°C when a chemical reaction occurs in water.
How many Joules of energy are absorbed?
12) As 19.00 grams of water are converted to water vapor at 100 C, calculate the Joules of energy absorbed.
13) If 0.500 gram of substance, H2CO3, is dissolved in a calorimeter with 150.0 grams of water, and the
temperature of the bath changes from 24.0 to 39.2C, how many Joules of energy were absorbed by the
water?
14) Calculate the constant for the heat of vaporization when 10.0 grams of ethanol are vaporized at its normal
boiling point.
Answers:
1) c
2) b
3) c
4) b
5) c
6) c
7) c
8) a
9) b
10) q = mHF
11) q = mc∆T
12) q = mHV
13) q = mc∆T
14) q = mHV
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D) Phase diagram: A graph which traces the change in entropy and enthalpy, during the physical
changes the substance undergoes with pressure as a function of temperature
Where heating / cooling curves generally illustrate temperature as a function of time (or time
of heating /cooling), the figure below shows an example of a phase diagram, which summarizes
the effect of temperature and pressure on a substance in a closed container. Every point in this
diagram represents a possible combination of temperature and pressure for the system.
1) The diagram is divided into 4 areas, which represent the solid, liquid, gaseous states of the
substance, and a supercritical zone … beyond the critical point.
Conditions = high pressure
& low temperature
Supercritical
Fluid
Conditions = low pressure
& low temperature
One good way to recall which area corresponds to each of these states is to remember the conditions of
temperature and pressure that are most likely to be associated with a solid, a liquid, & gas.


Low temperatures and high pressures favor the formation of a solid.
Gases, on the other hand, are most likely to be found at high temperatures and low pressures.

Liquids lie between these extremes.

Common components of a phase diagram are lines of equilibrium or phase boundaries, which refer to
lines that mark conditions under which multiple phases can coexist at equilibrium. Phase transitions
occur along lines of equilibrium.
Regardless of the substance, most phase diagrams are similar in construction and interpretation.
The conditions of the solid phase tend to be in the lower to upper left, the gaseous phase is represented
by the conditions of the lower right, and the liquid phase is in the middle.
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http://library.thinkquest.org/C006669/media/Chem/img/Graphs/Phase.gif
The triple point: * the temperature and pressure at which all three phases exist simultaneously
The critical point is that set of conditions above which distinct phases (e.g. liquid and gas) do not exist.
As the critical temperature is approached, the properties of the phases approach one another, resulting in
only one phase at the critical point, often referred to as a homogeneous supercritical fluid.

A supercritical fluid can effuse through solids like a gas, and dissolve materials like a liquid.

close to the critical point, small changes in pressure or temperature result in large changes in
density, allowing many properties of a supercritical fluid to be "fine-tuned".

Supercritical fluids are suitable as a substitute for organic solvents in a range of industrial and
laboratory processes. Carbon dioxide and water are the most commonly used supercritical
fluids, being used for decaffeination and power generation, respectively.
http://en.wikipedia.org/wiki/Supercritical_fluid
Phase Diagram of CO2
Phase Diagram of H2O
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Notice in the following diagram, that point “A” has been added and that there are two arrows. When
we follow “A” across the solid to gas boundary line, we can see, that there are two ways by which a
solid can sublimate.
A
Questions:
1) What is the most likely phase of the substance, at point A?
* gas phase
2) What is the phase of the substance represented by this phase diagram at STP? *liquid
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3) What would happen to the state of a substance represented by this phase diagram if the pressure
changed from Point A to Point B (holding temperature constant)?
* It would sublimate (undergo sublimation)
4) What phase change would be associated with moving directly from Point A to Point B on this phase
diagram?
*It
melts (fuses / goes from solid to liquid)
5) What
phase change would be associated with moving directly from Point B to Point A on this phase
diagram?
* The phase change is condensation
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6) At what approximate temperature will all 3 phases exist in equilibrium with each other?
* approximately 150K
7) The horizontal line on this phase diagram occurs at 1 atmosphere of pressure. What is the
normal freezing point of this substance?
*approximately 200 K
8) The horizontal line on this phase diagram occurs at 1 atmosphere of pressure. What is the
normal boiling point of this substance?
*approximately 425°K
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E) The Kinetic Molecular Theory of Matter (KMT)
1) Matter consists of extremely tiny particles (atoms, molecules, ions = “species”) that are
in constant motion.
2) In solids the species are paced closely together. Particles vibrate back and forth, essentially
“in place”
3) In liquids the species are arranged randomly, and as in gases, the species can move past and
around each other … thus each phase is described as a fluid.
4) Under normal conditions, the species of a gas are far apart. The gaseous particles (often
molecules), move rapidly in straight-line motion. The gas molecules collide with each other
and with the interior walls of the container holding the gas (creating a pressure).
a) The random motion of the gaseous molecules allows the gas molecules to occupy
the entire volume of the container. Hence, the volume of the gas sample is the
volume of the container!!!
5) A very important extension of the KMT is : Increasing temperature (average kinetic energy)
corresponds to faster and faster motions of the species. …
This means that a greater number of energetic collisions occur at higher temperatures, as
as rule.
A Generalized Maxwell-Boltzmann Energy Diagram: With a Constant Number of Gas Molecules
At lower temperature, only a few molecules under this curve have
enough energy to collide effectively to make bonds (shaded area in the
lower right.)
When temperature is increased, a greater number of molecules
possess sufficient average K.E. to collide effectively and to bond
(larger shaded area)
Note: Point A represents the necessary activation energy needed to
break the reactant species’ bonds and thus initiate a reaction.
Check Out: https://www.youtube.com/watch?v=66AxPceP5QY (up to 2:45 only)
Check out: For the shift in graph: https://www.youtube.com/watch?v=YnHIfqUZi48
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More Practice
1) An example of a physical property of a
compound, is it’s ability to:
6) Explain how freezing can be considered to be
an exothermic physical change. Be sure to
address both terms in your response.
1) react with an acid
2) react with oxygen
3) bond with with chlorine
4) dissolve in water
2) Which statement describes a chemical
property of the element magnesium?
1) Magnesium is malleable.
2) Magnesium conducts electricity.
3) Magnesium reacts with an acid.
4) Magnesium has a high boiling point.
3) Which property could be used to identify
a specific substance in the laboratory?
1) melting point
2) mass
7) Explain how boiling can be considered
endothermic?
3) temperature
4) volume
4) Which statement describes a chemical property
of hydrogen gas?
1)
2)
3)
4)
Hydrogen gas is colorless
Hydrogen gas has a density of 0.00009 g/cm3 at STP
Hydrogen gas has a boiling point of 20. K at 1 atm
Hydrogen gas burns in air
5) Which sample could occupy the volume of a 100 mL flask?
1) 25 cm3 Cu(s)
2) 30 cm3 CO2(g)
3) 50 cm3 SiO2(s)
4) 75 cm3 Fe(s)
Go on to the next page…
Multiple Choice Answers:
1) 4 2) 3 3) 1 4) 4 5) 2
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For questions 8 -10 use the following passage and your grasp of chemistry.
Carbon forms molecular compounds with some elements from Group 16. Two of these compounds are carbon dioxide,
CO2 and carbon disulfide CS2.
Carbon dioxide is a colorless, odorless gas at room temperature. At standard temperature and pressure, CO2(s) changes
directly to CO2(g), with a change in phase called sublimation.
Carbon disulfide is formed by a direct reaction of carbon and sulfur. At room temperature, CS2(s) is a colorless liquid
with an offensive odor. Carbon disulfide vapors are flammable.
8) Identify one physical property and one chemical property of CS2 at STP * colorless, liquid, offensive odor / flammable
9) State what happens to the potential energy of CO2 molecules as they undergo the sublimation change in phase.
* During sublimation (solid to gas), the potential energy increases
10) Is sublimation an exothermic or endothermic? * endothermic
Is sublimation a physical change or chemical reaction? *physical change
For questions, 11-14 use the following passage, your reference tables, and your understanding of chemistry.
Archimedes (287-212 BC), a Greek inventor and mathematician, made several discoveries important to science today.
He was related to Hiero of Syracuse, who ruled in Sicily, under the Romans. According to legend, King Hiero, asked
Archimedes to determine if a golden crown given as a gift, was indeed pure gold. The king suspected that the crown
consisted of a mixture (an alloy) of gold, with silver, tin, or copper.
Archimedes was completely flummoxed by the task. He could determine the mass, but the irregular shape of the crown
made the volume determination difficult. While getting into a bath, he noticed that his body forced the overflow of
water. He immediately realized his volume, displaced an equal volume of water …hence he had a means of
determining volume… Supposedly he ran naked through the streets yelling “Eureka” (I have found it!). The story
continues that he repeated the displacement procedure using the crown and equal masses of individual samples, of
gold, a sample of silver, one of tin, and one of copper. He then determined the ratio of mass to volume (density) of
each sample and the crown. Archimedes was able to determine that the crown was not made entirely of gold without
damaging it. In fact, it supposedly was equal masses of gold and silver.
11) Identify one physical property that Archimedes used in his comparison of the metal samples. *density
12) If Archimedes melted the crowns, would he have been testing a physical or chemical property? *physical
13) If Archimedes had rusted the crowns, would he have been testing a physical or chemical property? *chemical
14) Determine the volume of a 75.0 gram sample of gold at STP. Show your work, using E.S.A.
* Equation:
Density = Mass/Volume
19.3 g/cm3 = 75.0 g
x
x = 3.89 cm3
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