5.5 - Entropy

Question 1

Define entropy (ΔS)

Answer 1

a measure of the dispersal of energy within chemicals making up chemical system; greater = more disordered
units: JK-1mol-1

Question 2

Entropy rules

Answer 2

• at 0K there is no energy + all substances have entropy of 0
• solid->liquid->gas = melting/boiling increases randomness of particles more, so entropy is +
• more mol gas produced = disorder of particles increases, energy spread out more, so entropy is +

Question 3

Define standard entropy

Answer 3

the entropy of 1 mol of a substance under standard conditions (+)

Question 4

Equation for entropy change of reaction

Answer 4

entropy of products - entropy of reactants

Question 5

Define feasibility/spontaneity

Answer 5

whether a reaction is able to happen and is energetically feasible

Question 6

Define free energy change (ΔG)

Answer 6

overall energy change during a chemical reaction
- made up of enthalpy and entropy change
- to be feasible must be negative

Question 7

Equation for free energy change

Answer 7

ΔG = ΔH - TΔS

T = temp. in K

Question 8

Which processes can be shown to be feasible at room temp using ΔG?

Answer 8

endothermic reactions

Question 9

Why do many reactions with ΔG>0 not take place?

Answer 9

• very large Ea: can be overcome by using catalyst
• very slow rate (ΔG doesn’t take into account rate)