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Chemistry 30
Thermochemistry Notes
A1. Energy

____________________: the study of energy transfer and energy changes

___________________ and ___________________ are a major store of chemical energy that
we use in everyday lives.

the energy stored in the chemical bonds of hydrocarbons originally comes from
the ___________

ancient plants captured the energy of the sun during _______________________,
ancient animals ate the plants, then death and trapping in rock formations as oil,
gas, oil sand etc.

the First Law of Thermodynamics states that:
o the total energy of the universe is ____________________
o Energy is neither created nor destroyed, but can be transformed from
one form to another.
o ΔEsystem = - ΔEsurroundings

the Second Law of Thermodynamics states that:
o In every energy conversion, some energy is lost as heat (thermal
energy). Energy always flows from “hot to cold” or from high energy
source to low energy source.
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Chemistry 30
Thermochemistry Notes

Endothermic Reactions

In an endothermic reaction, the surroundings feel cooler.
o Example

Exothermic Reactions

In an endothermic reaction, the surroundings feel warmer.
o Example

IMPORTANT REACTIONS
o Photosynthesis
o
o Cellular Respiration
o
o Hydrocarbon Combustion
o
o

Note: water vapour formed when in open system, liquid water formed when in
closed system (bomb calorimeter).

there are two fundamental types of energy:
1. ________________ the energy of motion
2. ________________ energy that is stored
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Chemistry 30
Thermochemistry Notes

Fundamental forms of Energy
o Kinetic energy is the energy of motion.
o When there is a change in temperature, molecules speed up or slow down
therefore there is a change in kinetic energy.
o ex: when a gas is heated, the gas molecules increase their kinetic energy
and as a result move faster
o Heat = Thermal Energy = Kinetic Energy
o When there is no change in temperature, like melting and evaporating
there is a change in potential energy.

changes in ________________________________ take place during chemical reactions
when ____________________________________
___________________________________________________

chemical bonds are sources of __________________ potential energy

__________________ bonds ____________________ energy

__________________ bonds ____________________ energy

if the energy added to break the bonds is _________________ than the energy
released when the new bonds are formed then the reaction is
__________________________
eg)

endothermic changes are designated as ________________________ since energy is
being _______________ to the system

if the energy added to break the bonds is _____________ than the energy released
when the new bonds are formed then the reaction is _________________________
eg)
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Chemistry 30
Thermochemistry Notes

exothermic changes are designated as _________________________ since energy is
being ___________ by the system

the amount of energy lost or gained is _________________________
__________________________________ to the amount of substances that react
ie) if 100 g of a substance burning will release ___________________ energy compared
to when 50 g of that same substance burns
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Chemistry 30
Thermochemistry Notes
A2 Calculating Energy

________________________ is a measure of the ________________
________________________________ of the particles of a substance

the ________________ the particles are moving, the _____________ the temperature

the amount of energy needed to heat a substance depends on three factors:
1. the ______________ of the substance
2. the ________________________________________________
3. the ___________ of substance (heat capacity)

_____________ heat capacity is heat required to change the temperature of
____________________ of a substance by _________
where:
Q = heat energy in J
m = mass in g
Δt
c = specific heat capacity in J/gC
***found on pg 3 of data booklet
Example 1
Find the heat required to change 2.50 g of water from 10.0C to 27.0C.
Example 2
200g of a liquid solvent is heated up by 10K, with 4240 J of energy. What is the specific
heat capacity of the liquid?
 Workbook – PG 1 -2 All Qs
 Extra Practice – A1 & A2
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Chemistry 30
Thermochemistry Notes
A3 Enthalpy

The total of the kinetic and potential energy within a chemical system is called its
enthalpy. (Energy possessed by the system)

changes in enthalpy are related to changes in energy however and occur
whenever heat is released or absorbed in a physical, chemical or nuclear change …

Which means that we can use energy change (Q) from the system to the
surroundings to infer the change in enthalpy.
Changes in Enthalpy (Δ) = Changes in Energy (Q)
ΔrH = Q
KJ = KJ

Enthalpy change, ________, is measured in J or KJ

subscripts are sometimes used to denote the type of process, for example “r”
for “reaction”

_________ = enthalpy of reaction

the “” symbol is used to denote changes taking place at standard conditions

_________ = standard enthalpy of reaction (at SATP 100 kPa and 25C)

Molar enthalpy is the enthalpy change per mole of a substance

molar enthalpy is designated as rHm or Hm

molar enthalpy is measured in _____________________
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Chemistry 30
Thermochemistry Notes
Quick Practice/Concept Check
 If 2 moles of an unknown substance react and create 1200 J of energy, what is the
molar enthalpy of reaction for that substance?
Communicating Enthalpy Changes
Exothermic Reactions
1. Total Enthalpy rH Notation
 the total enthalpy (heat) of reaction can be given as a rH value ________________ of
the equation

the sign on rH is _____________________ since the enthalpy of the system is
________________________
eg)
2. Molar Enthalpy rHm Notation

the _____________________ (heat) of reaction can be given or determined from the
balanced chemical equation or amount of substance.

the sign on rH is negative in this cause communicating the enthalpy of the
system is decreasing (exothermic)
eg)
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Chemistry 30
Thermochemistry Notes
3. Total Enthalpy As a term Inside the Equation

in an exothermic reaction enthalpy is included as a _______________
eg)
4. Potential Energy Diagrams
 shows the potential energy of the __________________ and the __________________ of a
chemical reaction

reactants have _____________ potential energy than the products in an exothermic
reaction

the difference between the reactants and products is the __________
Exothermic
Products have__________ EP
than the reactants  energy has
been ____________ to the
surroundings
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Chemistry 30
Thermochemistry Notes
During an exothermic reaction, the
enthalpy of the system decreases and
heat flows into the surroundings.
We observe a temperature increase
in the surroundings.
Endothermic Reactions
1. Total Enthalpy rH Notation

the sign on rH is ____________________ since the enthalpy of the system is
__________________________
eg)
2. Molar Enthalpy rHm Notation

the sign on rH is _________________ since the enthalpy of the system is increasing
eg)
3. Total Enthalpy as a term Inside the Equation
 in an endothermic reaction enthalpy is included as a ______________
eg)
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Chemistry 30
Thermochemistry Notes
4. Potential Energy Diagrams
 reactants have ___________ potential energy than the products in an endothermic
reaction

the difference between the reactants and products is the ___________
Endothermic
Products have _________ EP
than the reactants  energy has
been ______________ by the
system
During an endothermic reaction,
heat flows from the surroundings
into the chemical system. We
observe a temperature decrease
in the surroundings.
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Chemistry 30
Thermochemistry Notes
 __________________-> energy is a product (right side of the equation)-> _____=
negative
 __________________->energy is a reactant (left side of the equation)-> _____= positive
 Workbook - Communicating Enthalpy Questions PG 3-4
 Extra Practice - A3 Communicating Enthalpy
F. Calculating Enthalpy Changes

molar enthalpy, in kJ/mol, and the number of moles of a substance can be used to
calculate the enthalpy change of a phase change:
where:
H =
n=
rH

=
the number of moles can either come from the __________________ in the
chemical reaction or from the formula

always have a sign on H or H
o ______________ for ___________________ (energy absorbed)
o ______________ for ___________________ (energy released)
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Chemistry 30
Thermochemistry Notes
Example 1
Calculate the molar enthalpy of combustion for oxygen given the following information:
2 C2H6(g) + 7 O2(g)  4 CO2(g) + 6 H2O(g)
cH = 2856.8 kJ
Example 2
Find the enthalpy change when 5.50 g of pentane burns. cH = 3244.8 kJ/mol
Example 3
When methane is burned, oxygen is consumed. Determine the mass of oxygen consumed
if the change in enthalpy is 250 kJ and the molar enthalpy of reaction for oxygen is
401.3 kJ/mol.
Workbook
 Workbook Pg 5-6 All Qs
 Extra Practice – A3 Calculating Enthalpy
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Chemistry 30
Thermochemistry Notes
A4 Calorimetry

calorimetry is a technological process of _______________________
________________________________________________________

the isolated system used to determine the heat involved in a phase change or in a
chemical reaction is called a _____________________
Calorimeter
Steps for Using a Simple Calorimeter
1. Measure the __________________________________ of the water in the calorimeter.
2. Add the ___________________ to the calorimeter.
3. Allow reaction to proceed, ________________ the solution to ensure even
temperature.
4. Measure the __________________________________ of the water in the calorimeter
(maximum temperature for exothermic reactions, minimum temperature for
endothermic reactions)

calorimetry is based on the First and Second Law of Thermodynamics…energy is
conserved and energy is transferred from hotter objects to cooler objects until
thermal equilibrium is reached

it is assumed that _______________________ is ________________
___________________________by the system except for the energy required or
released by the _________________________________
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Chemistry 30
Thermochemistry Notes

calculations are based on the Principle of Heat Transfer:

you must use a ____________ with you H values (either enthalpy change or molar
enthalpy)
endothermic = ___________________ value
exothermic = ____________________value
Example 1
A chemical reaction in a calorimeter causes the temperature of 500 g of water to increase
in temperature from 10.0C to 52.0C. Calculate the heat released by this reaction. Give
your answer in kJ.
Example 2
An 8.40 g sample of N2(g) is reacted with pure oxygen in a bomb calorimeter containing
1.00 kg of water to produce N2O. The temperature of the water dropped by 5.82C.
What is the molar heat of reaction of N2(g) in kJ/mol?
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Chemistry 30
Thermochemistry Notes
Example 3
A student built a simple calorimeter with a 25.0 g tin can and 150 mL of water. Calculate
the molar enthalpy of combustion of ethanol in kJ/mol if 0.166 g of this fuel increased the
temperature of the calorimeter by 7.00C. Remember to include not only the heat gained
by the water but also by the calorimeter.
Example 4
A student mixes 100.0 mL of 0.500 mol/L HBr(aq) with 100.0 mL of
0.500 mol/L
KOH(aq). The initial temperature of both solutions is 21.00C and the highest
temperature reached after mixing is 24.40C. Calculate the molar enthalpy of
neutralization in kJ/mol for the HBr(aq). Assume both solutions have the density and
heat capacity of pure water.
 Workbook PG 14 All Qs
 Extra Practice - A4 Calorimetry
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Chemistry 30
Thermochemistry Notes
A5 Hess’ Law: Predicting Enthalpy (rH) Changes

because of the law of conservation of energy, the heat of reaction is the
______________ whether the reactants are converted to the products in a
______________________________________ or in a
______________________________________________________

G.H. Hess (1840) suggested that if two or more __________________
__________________________ are ______________ to give a final equation then the
________________________ can be added to give the
_____________________________________________________

sometimes the heat of reaction for a chemical change is not easily measured due
to time of reaction, cost, rarity of reactants etc. so we use Hess’s Law to calculate
rH
Steps:
1. Write the __________________________________, if it is not given.
2. ________________________ the given equations so they will ______ to yield the
______________________________________.

if you multiply or divide an equation, multiply or divide the H by the
______________________________

if you flip an equation, __________ the sign on H
3. _________________ the reactants and products where possible to
______________________ (you must end up with your net equation!)
4. _________ the component enthalpy changes to get the ____________
______________________________
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Chemistry 30
Thermochemistry Notes
Example 1
Find the enthalpy change and draw the EP diagram for C(s, di)  C(s, gr) using the
following reactions:
C(s, gr) + O2(g)  CO2(g)
H = 393.5 kJ
C(s, di) + O2(g)  CO2(g)
H = 395.4 kJ
Example 2
Find the enthalpy change for H2O2(l)  H2O(l) + ½ O2(g) using the following
reactions:
H2(g) + O2(g)  H2O2(l)
H = 187.8 kJ
H2(g) + ½ O2(g)  H2O(l)
H = 285.8 kJ
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Chemistry 30
Thermochemistry Notes
Example 3
Find the heat of reaction for C(s) + 2 H2(g)  CH4(g) using the following reactions:
C(s) + O2(g)  CO2(g)
H = 393.5 kJ
H2(g) + ½ O2(g)  H2O(l)
H = 285.8 kJ
CH4(g) + 2 O2(g)  CO2(g) + 2 H2O(l)
H = 890.5 kJ
 Workbook PG 9-11 All
 Extra Practice A5 Hess’s Law – Additivity of Reaction Heats
Standard Heats of Formation fH

sometimes it is not easy to measure the heat change for a reaction (too
slow/expensive)

in this case, H can be determined using _______________________
____________________________________

heats of formation (fH) are the changes in EP that occur when
________________________________________________________

Hf for elements cannot be directly measured therefore they are designated as
__________…all other fH values are in reference to this…see pages 4-5 in data
booklet

the fH is an indirect measure of the _____________________ of a compound

the more ______________________________________________, the more
______________________________________________ (this means you have to add that
energy to decompose it)
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Chemistry 30
Thermochemistry Notes
eg)

List the following compounds in order from most stable to least stable.
H2O(l)
fH
=
C2H4(g)
fH
=
N2O4(g)
fH
=
PCl3(l)
fH
=
Al2O3(s)
fH
=
Hess’s Law formula states that the ________ is the difference between the
standard heats of formation of the __________________ and the
_______________________
rH =
Example 1:
Calculate the standard heat of combustion for 2 CO(g) + O2(g)  2 CO2(g) and draw the
EP diagram for this reaction.
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Chemistry 30
Thermochemistry Notes
Example 2:
Find the heat of combustion of ethane and draw the EP diagram for this reaction. The
products of combustion are gases.
Example 3
Calculate the molar enthalpy of combustion for ethane. The products of combustion are
gases.
Chem 30 Thermochemistry
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Chemistry 30
Thermochemistry Notes
Example 4
Calculate the energy released when 25.0 g of methanol is burned. The products of
combustion are gases.
Example 5
Calculate the molar heat of formation for ethylene glycol given the following information:
(CH2OH)2() + 5/2 O2(g)  2 CO2(g) + 3 H2O() H = 1178.0 kJ
 Workbook PG 7-8 & 12-13 All Qs
 Extra Practice A5 Hess’s Law – Additivity of Reaction Heats
Chem 30 Thermochemistry
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Chemistry 30
Thermochemistry Notes
A6 Energy and Efficiency

most of Canada’s energy (electricity) comes from ________________ processes such
as the combustion of ________________________

electricity is also generated through ____________________ processes

both methods involve changing ________________________________ (a _________________
change) which turns turbines to generate electrical energy

how does the energy from physical, chemical and nuclear processes compare:
o __________________ changes involve the breaking and forming of
___________________________ forces (__________ kJ/mol)
o _________________ changes involve the breaking and forming of
____________________________ (______________ kJ/mol)

_______________ changes involve changes within the
______________________________________________
(___________________________________________ of kJ/mol)

_____________________ is the ratio of _________________________ produced (energy
_____________) to ___________________________ in its production (energy _____________)
Chem 30 Thermochemistry
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Chemistry 30
Thermochemistry Notes

we have developed many technologies that help us to solve practical problems

it is important to be as ____________________ as possible with appliances and
vehicles

saving energy _________________________________ and it helps to
_____________________________________________ (greenhouse effect and acid rain)

in any process, the __________________________________________ that take place, the
________________________________ the process because of ______________________ in
transfer

gas furnace (natural gas) is about __________ efficient since it is used to
directly supply heat

natural gas power plant is only about __________ efficient because there are
several energy conversions that take place before electricity is generated
(water to steam to kinetic energy to mechanical energy to electrical
energy)
Fuelling Society

we must assess the _____________________________________ of relying on any fuel
source

when selecting an energy source, efficiency is not the only consideration

the _____________________________________________ must also be considered
Chem 30 Thermochemistry
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Chemistry 30
Thermochemistry Notes
Advantages vs. Disadvantages of Fossil Fuels
Advantages
Disadvantages









_______________ processes _______________ produce ___________
_____________________ but they do produce ___________________
______________________ which lasts for thousands of years

_________ turbines use a ______________________ energy source (sun indirectly) but
are not free of problems…they are _____________
___________________________________________________

______________________ power is also ____________________ but damming rivers
_________________________________________ on both sides of the dams

the amount of ____________ released by a fuel determines how __________________ it
is

fuels that use renewable energy sources (________________________
_________________________________________ etc.) and nuclear power are considered
the ________________________

___________________ is the _____________ fossil fuel and _______ is the
____________________________

regardless of which source of energy we use, we must think about the impact that
our fuels have on the environment
Your Assignment:
Chem 30 Thermochemistry
WB: PG 15 Q 3 (a,b,c)
24
Chemistry 30
Thermochemistry Notes
A7 Bond Energy and Activation Energy

bond energy is the energy ___________________________________
___________________________ or the energy __________________
_______________________________________________________

the ________________________________________________ of a reaction represents the
_____________________________ from _________________ the bonds in the reactant(s)
and _____________ the bonds of the product(s)

in _________________________ reactions, bond breaking absorbs ___________ energy
than the bond formation gives off, resulting in a ____________
Exothermic: H2(g) + Cl2(g)  2 HCl(g) + energy
Energy
(kJ)
Reaction Progress
Chem 30 Thermochemistry
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Chemistry 30
Thermochemistry Notes

in _______________________ reactions bond breaking absorbs ___________ energy
than the bond formation gives off, resulting in a ___________
Endothermic: 2 H2O() + energy  2 H2(g) + O2(g)
Energy
(kJ)
Reaction Progress

the energy barrier that must be overcome for a chemical reaction to occur is called
the _____________________________________

the atoms in the ________________have to be __________________ in order for them to
bond in a different configuration and become the products

the activation energy is always ______________ than the energy contained in the
reactants and the products, however the amount of activation energy necessary is
dependent on the reaction

the __________ of the activation energy barrier on a potential energy diagram
represents the _________________________________ of the reaction

in both endothermic and exothermic reactions, the molecules of the reactants are
moving with a certain amount of ___________________
_______________________
Chem 30 Thermochemistry
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Chemistry 30
Thermochemistry Notes

when the reactants _______________ with each other, the kinetic energy is
transformed into _____________________________

this potential energy is then stored in bonds of the chemical species that exists at
the top which is called the ________________________

this is a transitional species that is neither a reactant nor a product which has
_________________________________ and is ______________________________________

when the partial bonds of the activated complex re-form as chemical bonds in the
products, the stored potential energy is converted back into
__________________________________ as the product molecules
_____________________________
Chem 30 Thermochemistry
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Chemistry 30
Thermochemistry Notes
Potential Energy Diagram: Exothermic
Potential Energy Diagram: Endothermic
*
*
EP (kJ)
EP (kJ)
Reaction Progress
Reaction Progress
*
A8 Energy Diagrams and Catalysts

a catalyst is a substance that _________________________________ of a chemical
reaction ______________________________________ by the reaction

catalysts provide ________________________________ for chemical reactions

they ____________ the _______________________________ required for a reaction to
take place which results in the production of a
_____________________________________ of products in a given length of time (even
at a lower temperature)

catalyzed reactions can be shown on EP diagrams:
Potential Energy Diagram: Exothermic
Potential Energy Diagram: Endothermic
EP (kJ)
EP (kJ)
Chem
30 Thermochemistry
Reaction
Progress
28
Reaction Progress
Chemistry 30
Thermochemistry Notes
Catalysts in Industry

catalysts are often used in industry to speed up the reactions and obtain a
reasonable reaction rate under reasonable conditions

in cars, we have ________________________________ that use Pt(s), Pd(s) and Rh(s)
to speed up the combustion of exhaust gases so that more of the products are
_________________ (_______ instead of ______, _______ instead of ______)

the oil and gas industry uses catalysts (Pt(s), HF(aq), H2SO4(aq) etc) in the
______________________________________________ of _____________________ and
_________________ to make more marketable fuels like gasoline
Enzymes

compounds that act as catalysts in living systems are called __________________

called ________________________ catalysts

chemical reactions in the body occur at very _______ temperature (37C) and
without catalysts many would be too ___________
Your Assignment:
WB: PG 17-18 All Qs
Extra Practice: Extra Practice
Chem 30 Thermochemistry
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