Chemistry 30
Thermochemistry Notes
A. Energy
30-A1.2k  explain, in a general way, how stored energy in the chemical bonds of hydrocarbons
originated from the sun

we use hydrocarbons in many areas of our lives
eg) ____________________________________________________
_____________________________________________________________
___________________________________________

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.

there are two fundamental types of energy:
1. ____________________________________: the energy of
__________________ (of particles)
2. ____________________________________: energy that is
__________________ (in chemical bonds)

the First Law of Thermodynamics states that:
o the total energy of the universe is ____________________
o energy can be _______________________________________ however
the ____________________________ of any system is
_______________________ (it _________________ be created or
destroyed)

the Second Law of Thermodynamics states that:
o in the absence of energy input, a system becomes more
_______________________
o heat will always transfer from __________________________
_____________________________________________ until
__________________________________________ is reached
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B. Temperature Change
30-A1.1k  recall the application of Q = mct to the analysis of heat transfer

________________________ 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 = change in temperature in C
c = specific heat capacity in J/gC
***found on pg 3 of data booklet
Example
Find the heat required to change 2.50 g of water from 10.0C to 27.0C.
Your Assignment: pg 1 “Heat Calculations” #1-6
C. Energy and Enthalpy
30-A1.3k  define enthalpy and molar enthalpy for chemical reactions

____________________ is the sum of all forms of kinetic and potential energy in
a system (EK + EP)

unfortunately, the enthalpy of individual substances cannot be measured directly
(EK can with a thermometer but how do you measure EP?)
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
changes in enthalpy occur whenever heat is _____________________
______________________ in a ______________________________
__________________________________ …fortunately, this can be measured

_____________________________________________ is measured in
_________________

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 ___________ conditions
__________ = standard enthalpy of reaction (at SATP – 100 kPa and 25C)

________________________________ is the enthalpy change
_______________________ of a substance

molar enthalpy is also designated as H although we will be using just _______
for our formulas

molar enthalpy is measured in _______________________________
***this can be confusing so pay close attention to the context…wording and units!!!
D. Energy Change in Chemical Reactions
30-A1.10k  classify chemical reactions as endothermic or exothermic, including those for the processes
of photosynthesis, cellular respiration and hydrocarbon combustion
30-A1.9k  identify that liquid water and carbon dioxide gas are reactants in photosynthesis and products
of cellular respiration and that gaseous water and carbon dioxide gas are the products of
hydrocarbon combustion in an open system

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)
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
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)

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
E. Communicating Enthalpy Changes
30-A1.4k  write balanced equations for chemical reactions that include energy changes
30-A1.5k  use and interpret H notation to communicate and calculate energy changes in chemical
reactions
30-A1.3s  compare energy changes associated with a variety of chemical reactions through the analysis
of data and energy diagrams
Exothermic Reactions
1. rH Notation
 the 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. Inside the Equation

in an exothermic reaction enthalpy is included as a _______________
eg)
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3. 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
Endothermic Reactions
1. rH Notation
 the sign on rH is ____________________ since the enthalpy of the system is
__________________________
eg)
2. Inside the Equation
 in an endothermic reaction enthalpy is included as a ______________
eg)
3. Potential Energy Diagrams
 reactants have ___________ potential energy than the products in an endothermic
reaction

the difference between the reactants and products is the ___________
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Endothermic
Products have _________ EP
than the reactants  energy has
been ______________ by the
system
Your Assignment: pgs 1-2 “Energy Changes”
F. Calculating Enthalpy Changes
30-A1.5k  use and interpret H notation to communicate and calculate energy changes in chemical
reactions

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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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.
Your Assignment: pgs 2-3 “Enthalpy Changes” #1-7
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G. Calorimetry
30-A1.8k  use calorimetry data to determine the enthalpy changes in chemical reactions

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 _________________________________

calculations are based on the Principle of Heat Transfer:
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
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?
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.
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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.
Your Assignment: pg 3 “Calorimetry” #1-7
H. Industrial Bomb Calorimeters
 industrial calorimeters are used in _________________ to measure the heat of
combustion of food, fuel, oil, crops, and explosives

modern calorimeters have __________________________________ eg) volume
of water used, container (bomb) material, stirrer and thermometer

in calculating the energy of combustion, you take all components of the
calorimeter into account:
Etotal = mct (H2O) + mct (stirrer) + mct (thermometer) + mct (bomb)

all of the “mc” parts are constant so they are replaced by _______
_____________________________ the ________________________ of the
_______________________________ in _________________

you can also be asked to calculate _________ instead of kJ/mol in calorimetry
questions

you use the formula __________ instead on nH to give kJ/g
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Example 1
A 1.50 g sample of methane is completely burned in a calorimeter with a heat capacity of
11.3 kJ/C. The temperature increased from 20.15C to 27.45C. Calculate the molar
enthalpy of combustion for methane. Convert your answer to kJ/g.
Example 2
When 3.00 g of butter is burned in a bomb calorimeter with a heat capacity of 9.22 kJ/C
the temperature changes from 19.62C to 31.89C. Calculate the specific enthalpy of
combustion in kJ/g.
Your Assignment: pg 4 “Industrial Bomb Calorimetry” #1-3
I. Hess’ Law: Predicting Enthalpy (rH) Changes
30-A1.7k  explain and use Hess’ Law to calculate energy changes for a net reaction from a series of
reactions

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
_____________________________________________________
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
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 ____________
______________________________
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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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
Your Assignment: pgs 4-6 “Hess’s Law of Additivity”
J. Standard Heats of Formation fH
30-A1.6k  predict the enthalpy change for chemical equations using standard enthalpies of formation
30-A2.3s  draw and interpret enthalpy diagrams for chemical reactions

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)
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
=
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
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.
Example 2:
Find the heat of combustion of ethane and draw the EP diagram for this reaction. The
products of combustion are gases.
Your Assignment: pg 7 “Heats of Formation” #1
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Example 3
Calculate the molar enthalpy of combustion for ethane. The products of combustion are
gases.
Your Assignment: pg 7 #2-4
Example 4
Calculate the energy released when 25.0 g of methanol is burned. The products of
combustion are gases.
Your Assignment: pg 7 #5-7
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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
Your Assignment: pg 7 #8-10; pg 8
K. Energy and Efficiency
30-A1.1sts  explain that the goal of technology is to provide solutions to practical problems
30-A1.2sts  explain that technological problems often require multiple solutions that involve different
designs, materials and processes and that have both intended and unintended consequences

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)
o _______________ changes involve changes within the
______________________________________________
(___________________________________________ of kJ/mol)
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
_____________________ is the ratio of _________________________ produced
(energy _____________) to ___________________________ in its production
(energy _____________)

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)
Cheetos Combustion Lab
L. Fuelling Society
30-A1.2sts  explain that technological problems often require multiple solutions that involve different
designs, materials and processes and that have both intended and unintended consequences
30-A2.2sts  explain that the appropriateness, risks and benefits of technologies need to be assessed for
each potential application from a variety of perspectives, including sustainability

we must assess the _____________________________________ of relying on
any fuel source

when selecting an energy source, efficiency is not the only consideration
Chem 30 Thermochemistry
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
the _____________________________________________ must also be
considered
Advantages vs. Disadvantages of Fossil Fuels
Advantages

Disadvantages







30-A2.3sts  explain that the products of technology are devices, systems and processes that meet
given needs; however, these products cannot solve all problems

_______________ 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
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M. Bond Energy and Activation Energy
30-A2.1k  define activation energy as the energy barrier that must be overcome for a chemical reaction
to occur
30-A2.2k – explain the energy changes that occur during chemical reactions, referring to bonds breaking
and forming and changes in potential and kinetic 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
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)
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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
30-A2.3k  analyze and label energy diagrams of a chemical reaction, including reactants, products,
enthalpy change and activation energy

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 ___________________
_______________________

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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Potential Energy Diagram: Exothermic
Potential Energy Diagram: Endothermic
*
*
EP (kJ)
EP (kJ)
Reaction Progress
Reaction Progress
*
N. Catalysts
30-A2.4k  explain that catalysts increase reaction rates by providing alternate pathways for changes,
without affecting the net amount of energy involved

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)
Reaction Progress
Reaction Progress
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O. Catalysts in Industry
30-A2.1sts  explain that the goal of technology is to provide solutions to practical problems
 explain how catalysts, such as catalytic converters on automobiles, reduce air pollution
resulting from the burning of fuels

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
P. 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 ___________
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