Question

1. What is the entropy change for a pure solid melting into a liquid?

a. ΔS⁰_sys > 0

b. ΔS⁰_sys < 0

c. ΔS⁰_sys = 0

d. Need more information about the liquid to know

2. For a process where ΔH⁰_sys < 0 and ΔS⁰_sys> 0, when is the sign on ΔG⁰_sys < 0?

a. ΔG⁰_sys is never less than zero

b. ΔG⁰_sys < 0 for all temperatures

c. ΔG⁰_sys < 0 for low temperatures

d. ΔG⁰_sys < 0 for high temperatures

3. For a process where ΔH⁰_sys < 0 and ΔS⁰_sys< 0, when is the sign on ΔG⁰_sys < 0?

a. ΔG⁰_sys < 0 for high temperatures

b. ΔG⁰_sys < 0 for all temperatures

c. ΔG⁰_sys is never less than zero

d. ΔG⁰_sys < 0 for low temperatures

Answer 1

1. Entropy of solids is minimam , of liquids is more than solid but less than gases and of gases is maximum entropy .

Entropy is simply the randomness in the system.

So when solid melts to liquid , free movement of molecules increases and thus entropy increases.

And change in entropy = final entropy - initial entropy

As final entropy of liquid is more , so change is positive .

Thus ∆S°sys > 0 .

Option (a) is correct .