Download (Chapter 9 - Temperature)

(Chapter 9 - Temperature)
I. Temperature

Temperature is a REALTIVE indication of the average kinetic energy of the
molecules of a substance.
o It is not measured in units of energy (joules or calories) so it is NOT
energy, but it does indicate whether the KE is high or low.
o Temperature is NOT the same as Heat.

Heat IS A FORM OF ENERGY  it is the energy transferred from one object to
another due to a difference in temperature. (more on this later)
 Temperature Scales
o Celsius Temperature Scale  Based on the freezing point and boiling point of (pure) water
FP = 0°C
BP = 100°C
o
Fahrenheit Temperature Scale  based on the freezing point of (a super saturated solution of)
salt water.
Salt water FP = 0°F
Fresh water FP = 32°F
TF 
9
Tc  32
5
TC 
BP = 212°F
5
(TF  32 )
9
Absolute Temperature
The Kelvin Temperature Scale indicates the absolute temperature. This is a more
direct indication of the motion of the molecules of a substance.
The Kelvin Scale (absolute temperature) is based on ABSOLUTE ZERO
o
o
Absolute Zero is the temperature at which ALL MOLECULAR MOTION STOPS!
Can we get there?
o
Kelvin Scale  B/c it is a direct scale it is NOT measured in degrees!
0 K  absolute zero = no molecular motion
273 K  Fresh water freezes
373 K  Fresh water boils
TK = TC + 273
NOTE
Kelvin Scale  Gases
Celsius Scale  Solids and
Liquids
Fahrenheit  NEVER used in
calculations with the SI
system
II. Material Expansion
When a material is heated or cooled its dimensions will change. This is due to the
change in kinetic energy of the molecules.
How much it changes depends on:
1)
2)
Solids
Depending on the original shape of the solid, it can experience one of the following
changes
Example:
An aluminum meterstick is heated from 65°F to 95°F. What is the change in length?
b) What is the resulting length?
Example:
A square piece of metal with a hole cut out of its center is heated. As the temperature of the metal
increases will the hole get bigger, smaller or stay the same size? WHY?
Liquids
A liquid does not have a definite shape so when
heated it will always change in volume.
Example:
A Pyrex beaker is filled to the brim with 250 cm3 of water at 20°C.
a) How much does the water expand if it is heated to 60°C?
b) How much water actually overflows?
Gases
From chemistry you should recall that the pressure,
volume and temperature of a gas are all related.
For a constant temperature
Boyle’s Law 
P
P
P
For a constant pressure
Charles’s Law 
Just like solids and liquids, gases will contract when cooled and expand when heated
(due to the motion of the molecules).
Ideal Gas Law
We can combine Boyle’s Law and Charles’s Law into one statement known as the ideal
gas law. The ideal gas law can be expressed in two ways:
For a constant amount of gas:
For a constant pressure
For a given amount* of gas:
For a constant temperature
Example:
On a warm day (92°F), the air in a balloon occupies a volume of 0.20 m3 and exerts a pressure of 20 Lb/in2 (on the walls of
the balloon). If the balloon is cooled to 35°F the pressure decreases to 15 Lb/in 2. What is the resulting volume of the
balloon?
Example:
At an altitude of 10.0-km the atmosphere has an average temperature of -50°C and a pressure of 2.6 x 104Pa. Find the
MASS of hydrogen (H2) gas needed to fill a balloon whose volume at this altitude is to be 4000m 3.
You MUST be comfortable with the concept of the mole (see handout)
Example
How many moles of glucose are in 538 grams of glucose?
b) How many glucose molecules are in 538 grams of glucose?
Note: C6H12O6 = glucose.
Dealing with the mole
The basics:
Elements  the simplest substances of which matter is composed
 all matter is composed of elements
Atoms  the smallest particle of a given element
Compounds  the (chemical) combination of two or more elements
 has properties different from the elements from which is is composed
Molecules  the smallest particle of a given compound
Example: One molecule of water is the smallest amount of water you can
have and still have water. However, one water molecule is made up of
smaller pieces; one oxygen atom and two hydrogen atoms.
Hydrogen
atoms
Water
molecule
Oxygen
atom
Because atoms and molecules are such small particles, they have
very little mass. It may be inconvenient to express the mass of
such particles in traditional units (i.e. grams or kilograms).
Therefore atomic mass is usually expressed in terms of the
atomic mass unit (amu or just u), where;
1 atomic mass unit = 1 u = 1.66 x 10-27 kg
The mass of one proton (mp) = 1.007277 amu = 1.673 x 10-27 kg
The mass of one neutron (mn) = 1.008665 amu = 1.675 x 10-27kg
The mass of one electron (me) = 0.000549 amu = 9.11 x 10-31kg
We can find the atomic mass of any element using the periodic table.
For example:
Hydrogen has am atomic mass of 1.00794 amu.
1
Atomic number
Atomic symbol
H
1.00794
Atomic mass
The mole:
Technical definition  The mole is the amount of matter that contains as many particles as the
number of atoms in exactly 12grams of carbon12. The number of atoms in 12 grams of carbon12 is
6.0221367 x 1023 -- named Avogadro's number.
Simple definition  One mole of any substance contains 6.0221367 x 1023 (Avogadro's number)
particles of that substance. The particles can be atoms (for elements), molecules (for compounds)
or any other quantity (chemistry related or non-chemistry related).
For Example
 One mole of oxygen contains 6.0221367 x 1023 atoms of oxygen. (Relating the mole to elements/atoms)
 One mole of water contains 6.0221367 x 1023 molecules of water. (Relating the mole to
compounds/molecules)

One mole of gorillas contains 6.0221367 x 1023 gorillas. (You can relate the mole to anything – it is just a
unit indicating the amount of something)
For simplicity, we take Avogadro’s number to be N A = 6.02 x 1023 particles/mole
Molar mass:
A single carbon-12 atom has a mass of 12 amu. A single magnesium-24 (24Mg) atoms has
a mass of 24 amu; twice as massive as a carbon-12 (12C) atom. Because one mole always has the
same number of particles, one mole of 24Mg must be twice as massive as one ole of 12C. Because
one mole of 12C weighs 12 grams (by the definition of one mole), then one mole of 24Mg must
weight 24 grams. This indicates that the mass of a single atom of an element (in amu) is
numerically equal to the mass (in grams) of one mole of that substance. The mass of one mole
of a substance is called its molar mass.
For example:
One 12C atoms has a mass of 12 amu  one mole of 12C has a mass of 12 grams.
One nitrogen atom (14N) has a mass of 14 amu  one mole of 14N has a mass of 14 grams.
Molar mass also applies to compounds. To find the molar mass of a compound you must
first calculate its formula mass. The formula mass is the sum of the atomic masses of each atom in
the chemical formula.
For example:
Sucrose (table sugar) has a chemical formula of C12H22O11. This means that sucrose is made up of 12
atoms of Carbon, 22 atoms of Hydrogen and 11 atoms of Oxygen. To find its formula mass:
12 Carbon atoms have a mass of 
22 Hydrogen atoms have a mass of 
11 Oxygen atoms have a mass of 
(12 atoms)(12 amu) = 144 amu
(22 atoms)(1 amu) = 22 amu
(11 atoms)(16 amu)= 176 amu
This is the formula
mass.
One molecule of sucrose has a mass of  144 amu + 22 amu + 176 amu = 342 amu.
SO: One molecule of C12H22O11 has a mass of 342 amu  one mole of C12H22O11 has a mass of 342 grams.
This is the molar
mass.
(Chapter 9 - Heat)
I. Temperature vs Heat
Temperature
Heat IS a form of energy.
Heat
Heat Units
Joules (J) 


calorie (cal)  1 calorie is
Calorie (Cal) = kilocalorie 
British Thermal Unit (BTU) 
II. Heat Transfer
Heat cannot be possessed by a material; it is transferred from one object to another. The
amount of heat transferred to or from a material depends on:
1.
2.
3.
III. Calculating Heat Transfer - Calorimetry
Calorimetry is an experimentally based method for evaluating heat (energy) transfer
between materials.
Examples
Two convertibles are parked in the hot summer sun. The red car has leather seats and the blue car has cloth
seats (the fabric colors are the same). If Mr. Bruening, wearing his summer shorty-shorts, sits in the cars, in
which car will he burn the back of his legs? WHY?
A 100-gram piece of aluminum at 90°C is immersed in 1.0-L of water at 20°C. What is the final temperature of
the system once thermal equilibrium is reached?
In an experiment, 0.50-kg of a metal at 100°C is added to 0.50-kg of water at 20°C in an aluminum cup. The
cup has a mass of 0.25-kg. If the system comes to thermal equilibrium at 25°C, what is the specific heat
capacity of the metal?
IV. Phase Changes – Latent Heat
We know (from last chapter) that the state of matter depends on the (general) arrangement of its
molecules. More specifically, the state depends on the temperature* of the material and the pressure
exerted on it.
* recall that molecules at higher temperatures move more rapidly.
When a phase change occurs there is a transfer (addition or removal) of heat energy. However, during
a phase change this transfer of energy does NOT cause a change in temperature – all of the energy goes
into the phase change (rearrangement of the molecules).
We will consider phase changes at constant pressure.
Gaining energy
Losing energy
Solid
Liquid
Solid
Gas
Gas
In any change of Phase there is a transfer of energy.
Latent Heat of Vaportization (Lv) 
Latent Heat of Fusion (Lf) 
example:
How much heat is required to melt 500-grams of ice, initially at 0ºC? Is this heat gained or lost?
Example:
You remove a block of ice (1.50-kg) from a -6ºC
freezer. You wish to (eventually) vaporize all of
the material and super heat the steam to 120ºC.
How much energy is required?
Example:
Banana ice cream freezes at -2ºC and has a heat of fusion of 290 kJ/kg. When frozen its specific heat capacity is
1.9 kJ/kgºC and when melted its specific heat capacity is 3.3 kJ/kgºC.
a) A batch of ice cream is mixed at an initial temperature of 18ºC. How much heat is required to make 500-kg
of banana ice cream at -12ºC? Is this heat gained or lost?
b) How much refrigeration capacity (in kilowatts) is needed to do this in an 8-hour time frame?