Question

In which of the following cases entropy decreases?
A. Solid changing to liquid
B. Expansion of a gas
C. Crystal dissolve
D. Polymerisation

Answer 1

Hint: As we know that entropy is the randomness of the system, which is denoted by the symbol S. It is basically a state function, which is found to depend on the state of the system and not on the path that is followed.

Complete answer:
- As we know that as the entropy increases whenever heat flows from a hot object to a cold object.
- It is found that entropy increases when the ice melts, water is heated, water is boiled, and as water is evaporated. We can clearly see that when solids change into liquid there is an increase in entropy.
- As we know that when there is dissolution of crystal and expansion of a gas takes place there is an increase in entropy.
- In the polymerisation it is found that the number of molecules present is decreasing, the randomness decreases and hence, entropy also decreases.

- Hence, we can say that the correct option is (d), that is in Polymerisation, entropy decreases.

Note: - We should not get confused in the terms entropy and enthalpy. As, entropy is a property, which measures the randomness of the molecules. It is denoted by the symbol S.
- Whereas, enthalpy is a kind of energy, which is basically the sum of internal energy and flows energy. It is denoted by the symbol H.