Question

What happens if the entropy decreases ?

Answer 1

1. Entropy is the degree of randomness or measure of disorder.
2. According to Carnot cycle and for reversible processes , $$\begin{gathered} \sum _{}\frac{q}{T}=0 \\ whereqistheheat \\ andTisthetemperature \end{gathered}$$
3. $∆\mathrm{S}=\frac{\mathrm{q}}{\mathrm{T}}$
4. The overall entropy will always increase but it might happen that for a small part, heat transfer might decrease.
5. The entropy can be decreased for a phase change from gas to liquid to solid.
6. It might decrease for a reaction having number of moles less than the reactant side.
7. $∆\mathrm{G}=∆\mathrm{H}-\mathrm{T}∆\mathrm{S}$
8. If $∆\mathrm{S}$decreases that means $\mathrm{T}∆\mathrm{S}$ becomes less negative and for a endothermic reaction, since $∆\mathrm{H}$is positive so $∆\mathrm{G}$ becomes more positive and reaction will be non-spontaneous.
9. And for exothermic reaction $∆\mathrm{H}$ is negative hence the $∆\mathrm{G}$ becomes negative and is a spontaneous reaction.
10. According to the second law of thermodynamics, the entropy of an isolated system always increases.
11. And the universe is considered to be an isolated system.
12. As, the entropy of universe decreases then it will start shrinking.