Unit 6

Question 1

Thermodynamics

Answer 1

study of
energy and its conversion from
one form to another
* Thermodynamics is useful because it
has so many practical applications,
including predicting the direction of
chemical reactions.
* Among other things, this knowledge
helps us learn how to capture and
store energy efficiently
- a branch
of thermodynamics, which highlights
how heat is involved in chemical and
physical transformations

Question 2

There are two basic kinds of energy:

Answer 2

potential energy (Ep) and kinetic energy (Ek).
➢ The internal energy, E, of a system is the sum of all energy
(potential and kinetic) of everything in that system.
EK is the energy of motion = 1/2 mv2EP is stored energy

Question 3

chemical bond energy

Answer 3

potential energy stored in molecular bonds
- Many of our cellular processes are
driven by energy released upon hydrolysing a
phosphate bond in an adenosine triphosphate
(ATP) molecule to create more stable
products: ADP and inorganic phosphate

Question 4

energy of molecular motion

Answer 4

• translational, rotational and vibrational
• sometimes also called “thermal energy”
• temperature is a common measure of the energy of mol. motion

Question 5

Energy and Change in Energy

Answer 5

Energy - the capacity to do work or supply heat
Change in energy = work plus heat

Question 6

First law of thermodynamics

Answer 6

Energy cannot be created or destroyed (although as we will discuss,
energy can be converted from one form to another)
- Note that is the total energy of the universe that is conserved

Question 7

System

Answer 7

The system is chosen to include whatever you are focusing on
(and things that cannot usefully be separated from that)

Question 8

Surroundings

Answer 8

The surroundings is everything not in the system.
System + Surroundings = Universe
- If energy leaves the system, it must enter the surroundings (and visa
versa). Thus, we can determine the energy change of a system of
interest by measuring the energy change in the surroundings.

Question 9

Change in energy

Answer 9

Any change in the energy of the system must be accompanied by
an equal magnitude change in the energy of the surroundings,
but the signs of these changes must be opposite.
∆𝐸𝑢𝑛𝑖𝑣𝑒𝑟𝑠𝑒 = ∆𝐸𝑠𝑦𝑠𝑡𝑒𝑚+∆𝐸𝑢𝑟𝑟𝑜𝑢𝑛𝑑𝑖𝑛𝑔𝑠= 0
e.g., if a reaction occurs in a beaker of water and the temperature of
the water increases, we can deduce that the reaction produced heat.
Moreover, if we can determine how much heat flowed into the water,
we know how much heat the reaction produced

Question 10

Barrier

Answer 10

For practical reasons, we often use a barrier to limit the surroundings
in thermochemical experiments. Its role is to stop (or at least
minimize) transfer of energy (heat and work).
Thus, we can determine the energy change in system of interest
by measuring energy change in limited, well-defined surroundings

Question 11

Sign Conventions

Answer 11

In thermodynamics, all signs reflect the system’s perspective

Question 12

State function:

Answer 12

A function or property whose value depends
only on the present state (condition) of the system.
Stated another way… the path does not matter

Question 13

Energy

Answer 13

the capacity to do work or supply heat

Question 14

heat

Answer 14

also called “thermal energy”) will flow from
higher-temperature objects to lower-temperature objects

Question 15

Work

Answer 15

Mechanical work is the product of force (F) and
distance (d).
w = F × d
- The larger the required force, or the longer the distance an
object is moved, the more work is done on it

Question 16

expansion work

Answer 16

Gas forming reaction in an insulated container that is attached to
a piston-cylinder assembly that pushes against something
- The system pushes the piston out,
doing work on the surroundings.
The system releases (loses) energy.

Question 17

Pressure Volume

Answer 17

Expansion work is also often known as pressure volume (PV) work,
because the amount of work done depends on both P and V
* At constant pressure (P = Psurr),
𝑤 = −𝑃∆𝑉 = −𝑃 (𝑉𝑓𝑖𝑛𝑎𝑙 − 𝑉𝑖𝑛𝑖𝑡𝑖𝑎𝑙)
➢ More work is done when the volume change (DV) is larger
and/or when pushing against a higher external pressure

Question 18

Expansion works = units

Answer 18

You will have many opportunities to calculate PV work in the
homework, problem solving sessions and tutorials.
* For this, it will be useful to realize that the units of work, heat
and energy must be the same. In SI, they are in Joules (or in kJ).
* Here is a handy conversion between Joules and our most
commonly used units of pressure and volume:
101.3 𝐽 = 1 atm.× 𝐿

Question 19

Expansion work

Answer 19

𝑤 = −𝑃∆𝑉
-The negative sign is required to fit with the convention that signs
reflect the system’s perspective.
Consider a system that expands against a pressure
-P, which is the constant pressure of the surroundings, is always > 0.
* The system does work. It loses internal energy by doing this work.

Question 20

Internal Energy (E)

Answer 20

is transferred as heat and work (w)

Question 21

Enthalpy

Answer 21

is a useful scale for keeping track of the energetics of these
constant-pressure transformations, in the kitchen or on the benchtop
H=E+PV

Question 22

Change in Enthalpy

Answer 22

is equal to the amount of heat absorbed or released in a transformation
(a real or imagined reaction) at constant pressure (see next slide). This means
enthalpy change (DH) is often straightforward to determine via experiment

Question 23

Exothermic

Answer 23

Evolved heat flows out
of the system into the
surroundings. Heat is a
product of the reaction

Question 24

Endothermic

Answer 24

Heat flows into the system
from the surroundings. Heat
is a reactant

Question 25

Heat capacity

Answer 25

s the amount of heat (q, or
DH) required to raise
the temperature of an object or substance by 1 °C (or 1 K)
-Things with a high heat capacity require a lot of heat to
increase in temperature. Conversely, these also give off a lot of
heat when they cool down. In essence, high heat capacity
materials act as a good sponge for (or, store of) thermal energy.
In contrast, materials with low heat capacity heat up easily (and
cool down easily), absorbing (and giving off) little heat as they
do so
-The energy (from heat, q) excites both
translational motion of molecules and
vibrations and rotations within and
between molecules

Question 26

Specific Heat Capacity

Answer 26

heat capacity per mass (1.00 g)

Question 27

Molar Heat Capacity (C or Cm)

Answer 27

heat capacity per mole

Question 28

Calorimetry

Answer 28

is the science of measuring the heat exchanged in
chemical reactions.
-In calorimetry, the heat of reaction (qrxn) is measured indirectly
by means of a calorimeter. If the reaction produces heat, the
temperature of the surroundings increases and visa versa

Question 29

Bomb calorimeters

Answer 29

are commonly used to
measure heat of combustion reactions.

Question 30

Standard States

Answer 30

Standard states are used as a reference condition, so we can usefully
* tabulate Standard Enthalpies of Formation (∆𝑯𝒇𝒐) and
* use these to calculate and compare to Standard Enthalpies of
Reaction (∆𝑯𝒓𝒙𝒏)

Question 31

Standard States (according to Chemists)

Answer 31

pure substance: most stable form at 1 atm
* gas: 1 atm and ideal behavior
* substance in aqueous solution: 1 M conc.
All at a specified temperature, which is usually 25 °C

Question 32

• Standard Enthalpies of Formation (DH°f):

Answer 32

The enthalpy change
for the formation of 1 mole of substance in its standard state
from its constituent elements in their standard states

Question 33

The bond energy

Answer 33

The heat released or absorbed during a
chemical change is due to differences between reactant and
product bond energies (BE)
Breaking bonds requires energy
forming bonds gives off energy