Entropy and Free Energy

Question 1

What is entropy?

Answer 1

A measure of the amount of disorder of a system.

Question 2

What does a high entropy mean?

Answer 2

There will be more disorder/dispersal.

Question 3

What are the units for entropy?

Answer 3

JK-1 mol-1.

Question 4

What is the trend of entropy in solids, liquids and gases?

Answer 4

• Solids have the smallest entropy.
• Liquids have greater entropies.
• Gases have the greatest entropies.

Question 5

What is the entropy at 0K?

Answer 5

There would be no energy and all substances would have an entropy value of zero.

Question 6

How does the entropy value change as the system changes to be more random?

Answer 6

Energy can be spread out more so there will be an entropy change which will be positive.

Question 7

How does the entropy value change as the system changes to be less random?

Answer 7

Energy becomes more concentrated and so the entropy change will be negative.

Question 8

What happens when substances change state from solid to liquid to gas have an increased entropy?

Answer 8

The melting points and boiling points increase the randomness of the particles and so energy is more spread out so the change is positive.

Question 9

How can you predict entropy values by just the number of molecules?

Answer 9

If there are less gas molecules in the products than the reactants, there is a more negative entropy value.

Question 10

What is the standard entropy (S)? Units?

Answer 10

The entropy of one mole of substance, under standard conditions - JK-1 mol-1.

Question 11

What entropy value is standard entropy always?

Answer 11

Positive.

Question 12

What is the standard entropy equation?

Answer 12

(Sum of standard entropy of products) - (Sum of standard entropy of reactants).

Question 13

What is feasibility?

Answer 13

Used to describe whether a reaction is able to happen and is energetically feasible.

Question 14

What is free energy change (G)?

Answer 14

The overall change in energy during a chemical reaction.

Question 15

What are the 2 types of free energy (G)?

Answer 15

1. Enthalpy change H - the heat transfer between the chemical system and the surroundings.
2. The entropy change at the temperature of the reaction TS - the dispersal of energy within the chemical system itself.

Question 16

What is the Gibbs’ equation?

Answer 16

G = H = TS:
- T is the temperature in kelvin.

Question 17

What is the condition that a reaction is feasible?

Answer 17

There must be a decrease in free energy (G).

Question 18

What must the values in the Gibbs’ equation be?

Answer 18

Kj K-1 mol-1.

Question 19

How do you work out the minimum temperature for feasibility?

Answer 19

Use the equation:

H - TS = 0.

Question 20

Can endothermic processes also be feasible?

Answer 20

Yes, at room temperature, you need to calculate G from the Gibbs’ equation using the temperature given in kelvin and prove that it is a negative number, so reaction is feasible.

Question 21

What is the limitation of predictions made for feasibility?

Answer 21

Many reactions have a negative G and still do not seem to take place.

Question 22

Why do some reactions with negative G values not take place/are not feasible?

Answer 22

Because of the very high activation energy resulting in a slow rate, so DOES NOT TAKE INTO ACCOUNT OF THE KINETICS OR RATE OF THE REACTION.