15.2 Entropy

Question 1

Define entropy

Answer 1

ENTROPY (S): measure of distribution of total available E between particles (measure of disorder)

ΔS in JK^-1mol^-1

Based on Second Law of Thermodynamics - energy disperses - increase in entropy in universe

Question 2

ΔS equation in reaction

Answer 2

ΔS = Σ S _prod. - Σ S _react.

Question 3

Factors which affect increase in entropy

Answer 3

Entropy increases as:

1. Increase in temperature: temp incr - entropy inc
2. Change of state of mattter: solid < liquid < gaseous
3. Increase in number of particles increases entropy
4. Mixing particles
5. Increase in volume - decrease in pressure

Question 4

Change in entropy of surroundings and change in enthalpy of a system

Answer 4

ΔS in surrounding is -ΔH in system: E leaves system - increases entropy in surrounding

Question 5

Calculating total entropy changes

Answer 5

Explain how endothermic reactions can occur - change in entropy of a system compensates for the negative change in entropy in surrounding (heat flows from surroudning to the system)

Question 6

Explain Gibbs free E

Answer 6

Gibbs free E measures feasibility of a reaction (combination of enthalpy and entropy)

ΔG_system = ΔH_system - T x ΔS_system

ΔG < 0 spontaneous (negative ΔG favours products)

ΔG > 0 non-spontaneous

Question 7

Gibbs free E calculation equations

Answer 7

ΔG_system = ΔH_system - T x ΔS_system

ΔG_reaction = Σ ΔG_{f (prod.)} - ΔGf (react.)

Question 8

Relationship between Gibbs free E and equilibrium shift or a reaction

Answer 8