The Second Law of Thermodynamics

Question 1

State the two statements of the Second Law of Thermdynamics

Answer 1

• Spontaneous processes are those that increase the total entropy of the universe
• The entropy of an isolated system increases during any spontaneous process

Question 2

What is a spontaneous process

Answer 2

Is one which has a natural tendency to occur
One started will continue without any intervention
Move towards their equilibrium state (completion) without any external influence
Note: this does not mean that the process occurs at a significant rate

Question 3

What is entropy

Answer 3

Is a measure of randomness or disorder in a system

Question 4

What is the equation for working out the entropy for an overall reaction

Answer 4

ΔS = S.final - S.inital

Question 5

What is meant by adding heat ‘reversibly’

Answer 5

means that heat is added very slowly, so that at any stage the temperature difference between the system and its surroundings is tiny and is always close to thermal equilibrium

Question 6

Entropy is a …. function

Answer 6

state

Question 7

What is the equation to work out the entropy change using temperature

Answer 7

Question 8

What does this equation for entropy tell us

Answer 8

• If a lot of energy is transferred as heat (qrev) then there is a large increase in entropy
• There is a greater increase in entropy if this transfer occurs at low temperatures

Question 9

What is the benefit of entropy being a state function

Answer 9

So if we can’t find a reversible path between the inital and final states, we can calculate the entropy change even if that route does not occur in practice

Question 10

What are the units for entropy and the units of molar entropy

Answer 10

J K⁻¹
J mol⁻¹ K⁻¹

Question 11

Moving from a solid to liquid, and then liquid to gas, how does entropy change

Answer 11

Entropy increases

Question 12

True or false?
the entropy of that substance changes even as its temperature stays the same

Answer 12

true
This is a phase change

Question 13

If a phase transition takes place at constant pressure then the heat supplied can be equated with the change in enthalpy
What is the equation for this

Answer 13

ΔS = ΔH / T

Question 14

Entropy change is related to the heat capcity
State an equation which shows this

Answer 14

Question 15

The Boltzmann entropy formula can be used to work out the absolute values of entropy for substances using molecular statistics
What is the equation for this

Answer 15

S = Kb In(W)

Kb = Boltzmann constant
W = number of ways of arranging molecules and their energies

Question 16

What is residual entropy

Answer 16

For soldids at T=0 K, there is no thermal motion of the molecules and the disorder arises from the number of possible oritentations a molecule can take up in the crystal