3.7 Entropy and feasibility

Question 1

What is entropy and how is it measured?

Answer 1

The measure of disorder in a system
measures as S in Jk-1mol-1

Question 2

What state has the highest entropy?

Answer 2

Gas
higher than liquid that’s higher than solid

Question 3

What is the equation to find S from absolute entropy values?

Answer 3

ΔS = Sfinal – Sinitial

Question 4

What are the ways to determine the change of entropy from an equation?

Answer 4

If there is only gas on one side entropy is more that way
the more mols of gas on one side

Question 5

How does entropy change from left to right?

Answer 5

More on right -ΔS
More on left +ΔS

Question 6

What is the Gibbs equation?

Answer 6

ΔG = ΔH – TΔS

Question 7

What are the units in the Gibbs equation?

Answer 7

KJMol-1
ΔS in J so must /1000

Question 8

When are reactions feasible? (ΔG)

Answer 8

When ΔG is negative
ΔG = 0 is point of feasibility

Question 9

How can we predict that a reaction will never be feasible?

Answer 9

An endothermic reaction (+ΔH) with a -ΔS means ΔG is always +ve so cannot exist

Question 10

How can we predict that a reaction will always be feasible?

Answer 10

Exothermic (-ΔH) with a +ΔS means ΔG will always be negative

Question 11

What conditions are required for a reaction to sometimes be feasible?

Answer 11

Exothermic (-ΔH) with -ΔS when T is small
or Endothermic (+ΔH) with +ΔS when T is large