8: Entropy and Gibbs Free Energy

Question 1

What is entropy?

Answer 1

A measure of how much disorder or chaos there is.

Question 2

What does it mean if something is high in entropy?

Answer 2

There is more disorder.

Question 3

Which state of a substance would have the most entropy?
Why?

Answer 3

Gases, they have the most energy and are free to quickly move around.

Question 4

Generally, how is entropy as a whole changing in the universe?
Give an example using a glass.

Answer 4

Entropy is always increasing.
For example, glass could shatter, increasing its entropy, but could never fit itself back together.

Question 5

Give the formula for calculating entropy change.

Answer 5

S = entropy of products - entropy of reactants

Question 6

Give the units for entropy.

Answer 6

J K-1 mol-1

Question 6

Give the units for enthalpy change.

Answer 6

Kj-1 mol-1

Question 6

What minimum Gibbs free energy value is usually required for a reaction to be feasible?

Answer 6

It must be 0 or negative.

Question 7

Give the equation used to calculate enthalpy change.

Answer 7

Enthalpy change = products - reactants

Question 7

What is gibbs free energy used for?

Answer 7

It predicts whether a reaction is feasible or not.

Question 7

What is a feasible reaction?

Answer 7

A reaction that continues fully to completion.

Question 8

What 2 factors, aside from a negative Gibbs free energy value, can affect reaction feasibility?

Answer 8

High activation energy
Slow rate of reaction

Question 8

Give the equation for Gibbs free energy.

Answer 8

DeltaG = Delta H - TdeltaS

Question 9

Give the formula for finding the temperature a reaction becomes feasible at.

Answer 9

T = enthalpy change / entropy change

Question 10

If a reaction is exothermic, will enthalpy change be positive or negative?

Answer 10

Negative enthalpy change

Question 11

If a reaction is endothermic, will the enthalpy change be positive or negative?

Answer 11

Positive enthalpy change

Question 12

If a reaction is exothermic (negative enthalpy change) and has a negative TdeltaS value, when will the reaction be feasible (high/low temperatures)
How do low and high temperatures effect the size of the entropy change?

Answer 12

It will be feasible at low temperatures
It will not be feasible at high temperatures.
Low temperatures will create a small positive entropy change.
High temperatures will create a a large positive entropy change

Question 13

If a reaction is exothermic (negative enthalpy change) and has a positive TdeltaS value, when will the reaction be feasible?

Answer 13

The reaction is always feasible as delta G is always negative.

Question 14

If a reaction is endothermic (positive enthalpy change) and has a negative TdeltaS value, when will the reaction be feasible?

Answer 14

The reaction is NEVER feasible, regardless of temperature as delta G is always positive.

Question 15

If a reaction is endothermic (positive enthalpy change) and has a positive TdeltaS value, when will the reaction be feasible? (high/low temperatures)
How do low/high temperatures effect the size of the entropy change?

Answer 15

The reaction will be feasible at high temperatures.
It is not feasible at low temperatures.
At high temperatures, the overall entropy change is a large negative number.
At low temperatures, the entropy change is a small negative number.

Question 16

How does higher temperature affect delta G and entropy change?

Answer 16

Higher temperature makes delta G more negative so entropy change gets bigger.