AP Chemistry
Singapore American School
LECTURE NOTES
Based on “Chemistry” by Zumdahl, 7th Edition
All diagrams are from ‘Chemistry’ by Zumdahl, 7th Edition
Unit 5: Thermochemistry
Chapter 6 THERMOCHEMISTRY
In chemistry energy is a vitally important consideration!
So how do we define energy?
Easy!
Energy is the ability to do work or produce heat
In this unit we look specifically at chemical reactions that either require an input of heat
energy to run, or reactions that release heat as a factor the reaction/
In other words, we’ll study the relationship between energy and chemical reactions.
On the largest scale, consider, the total amount of energy in the universe is constant.
Another key piece of knowledge is that energy is conserved!
The Law of Conservation of Energy (also known as the First Law of Thermodynamics)
is nothing new.
Energy cannot be created or destroyed, but merely transformed from one
form to another
When energy is transformed (e.g. from light energy to chemical energy) we call this an
energy transformation
But when we say heat energy moves from a warm liquid in the beaker in the lab into the
glass of the beaker itself then we call that an energy transfer.
It’s the same energy (heat) just moved from one substance to another.
The natural movement of heat energy is always almost always from an area of high heat
energy (something hot) to an area of low heat energy levels (something cold).
, Unit 4 - Chapter 6 - Thermochemistry
Page 2/55
When we start a conversation about energy though, there are TWO types of energy that
are the most important. These are the two groups into which all other types of energy
can be classified.
There two types of energy are:
● Kinetic (KE) the energy of motion or movement
any moving object is said to have KE
amount of KE is dependant on the mass (m) of an object
and its velocity (v)
2
Formula: KE = mv
2
mass in grams (g)
velocity in meters per second (m/s)
● Potential (PE) this is stored energy
energy stored in an object because of its position
it could be its position in terms of shape (a coiled string
has PE as work was done in it to coil it up in the first
place)
or it could be due to its position above the earth if work
was done to an object to elevate it above the earth
this last type of referred to an gravitational potential
energy (GPE)
amount of GPE depends on the mass (m) of the object,
the acceleration due to gravity (g) and the height (h) that
the object is elevated to
Formula: GPE = mgh
mass in grams (g)
Acceleration due to gravity 9.8 m/s/s
height in meters (m)
Unit of energy is the same, irrespective of what type we are talking about
The SI unit for energy is one we have already met.
The unit of energy is the Joule (J)
, Unit 4 - Chapter 6 - Thermochemistry
Page 3/55
You need an energy source in order to do work.
We defined energy as the ability to do work.
So it makes sense to think that the units we use for energy are also the ones we do use
for work.
Work is defined as the application of a force through a distance.
To carry this out you need energy!
So if you perform 100 J of work we c=say that you have spent 100 J of energy.
As an equation: Work = Force x distance
W = Fd
consider Force is measured in Newtons (N)
Distance is measured in meters (m)
So looking at the units and the equation then
1 Joule = 1 Newton · meter
I J = 1 Nm
There is a concept called a state function (or a state property).
This simply means that the value is the same all the time and it is not influenced by other
factors, or is not dependent on other factors
A state function will always be the same.
Energy is a state function (e.g. the level of energy required to excite a ground state
electron to the next energy level is a state function that is always a set finite amount)
On the other hand, work and heat are NOT state functions as they can vary
significantly due to outside factors that be manipulated
, Unit 4 - Chapter 6 - Thermochemistry
Page 4/55
In every chemical reaction there is at least one reactant (original arrangement of atoms)
and one product (the new arrangement of atoms).
In all chemical reactions two (2) things always happen:
1. Matter (atoms) is rearranged
2. Energy is involved in some way
Energy (E), measured in Joules (J)
A change in energy is shown as ΔE where Δ is the Greek symbol (capital) for delta,
which means a change
ΔE can be positive (+ΔE) or negative (-ΔE)
If a reaction has a +ΔE that means that it requires energy in order to proceed.
On the other hand if the reaction has a -ΔE then the reaction will release heat to
its surroundings and the products will have less energy than the reactants.
In terms of energy and chemical reactions there are two (2) basic types of reactions:
1. Exothermic these reactions release energy to their surroundings
the reactants has more energy than the products do
energy was lost to the surroundings
-ve ΔE
Singapore American School
LECTURE NOTES
Based on “Chemistry” by Zumdahl, 7th Edition
All diagrams are from ‘Chemistry’ by Zumdahl, 7th Edition
Unit 5: Thermochemistry
Chapter 6 THERMOCHEMISTRY
In chemistry energy is a vitally important consideration!
So how do we define energy?
Easy!
Energy is the ability to do work or produce heat
In this unit we look specifically at chemical reactions that either require an input of heat
energy to run, or reactions that release heat as a factor the reaction/
In other words, we’ll study the relationship between energy and chemical reactions.
On the largest scale, consider, the total amount of energy in the universe is constant.
Another key piece of knowledge is that energy is conserved!
The Law of Conservation of Energy (also known as the First Law of Thermodynamics)
is nothing new.
Energy cannot be created or destroyed, but merely transformed from one
form to another
When energy is transformed (e.g. from light energy to chemical energy) we call this an
energy transformation
But when we say heat energy moves from a warm liquid in the beaker in the lab into the
glass of the beaker itself then we call that an energy transfer.
It’s the same energy (heat) just moved from one substance to another.
The natural movement of heat energy is always almost always from an area of high heat
energy (something hot) to an area of low heat energy levels (something cold).
, Unit 4 - Chapter 6 - Thermochemistry
Page 2/55
When we start a conversation about energy though, there are TWO types of energy that
are the most important. These are the two groups into which all other types of energy
can be classified.
There two types of energy are:
● Kinetic (KE) the energy of motion or movement
any moving object is said to have KE
amount of KE is dependant on the mass (m) of an object
and its velocity (v)
2
Formula: KE = mv
2
mass in grams (g)
velocity in meters per second (m/s)
● Potential (PE) this is stored energy
energy stored in an object because of its position
it could be its position in terms of shape (a coiled string
has PE as work was done in it to coil it up in the first
place)
or it could be due to its position above the earth if work
was done to an object to elevate it above the earth
this last type of referred to an gravitational potential
energy (GPE)
amount of GPE depends on the mass (m) of the object,
the acceleration due to gravity (g) and the height (h) that
the object is elevated to
Formula: GPE = mgh
mass in grams (g)
Acceleration due to gravity 9.8 m/s/s
height in meters (m)
Unit of energy is the same, irrespective of what type we are talking about
The SI unit for energy is one we have already met.
The unit of energy is the Joule (J)
, Unit 4 - Chapter 6 - Thermochemistry
Page 3/55
You need an energy source in order to do work.
We defined energy as the ability to do work.
So it makes sense to think that the units we use for energy are also the ones we do use
for work.
Work is defined as the application of a force through a distance.
To carry this out you need energy!
So if you perform 100 J of work we c=say that you have spent 100 J of energy.
As an equation: Work = Force x distance
W = Fd
consider Force is measured in Newtons (N)
Distance is measured in meters (m)
So looking at the units and the equation then
1 Joule = 1 Newton · meter
I J = 1 Nm
There is a concept called a state function (or a state property).
This simply means that the value is the same all the time and it is not influenced by other
factors, or is not dependent on other factors
A state function will always be the same.
Energy is a state function (e.g. the level of energy required to excite a ground state
electron to the next energy level is a state function that is always a set finite amount)
On the other hand, work and heat are NOT state functions as they can vary
significantly due to outside factors that be manipulated
, Unit 4 - Chapter 6 - Thermochemistry
Page 4/55
In every chemical reaction there is at least one reactant (original arrangement of atoms)
and one product (the new arrangement of atoms).
In all chemical reactions two (2) things always happen:
1. Matter (atoms) is rearranged
2. Energy is involved in some way
Energy (E), measured in Joules (J)
A change in energy is shown as ΔE where Δ is the Greek symbol (capital) for delta,
which means a change
ΔE can be positive (+ΔE) or negative (-ΔE)
If a reaction has a +ΔE that means that it requires energy in order to proceed.
On the other hand if the reaction has a -ΔE then the reaction will release heat to
its surroundings and the products will have less energy than the reactants.
In terms of energy and chemical reactions there are two (2) basic types of reactions:
1. Exothermic these reactions release energy to their surroundings
the reactants has more energy than the products do
energy was lost to the surroundings
-ve ΔE
