Question

Which of the following endothermic processes are spontaneous?
A. Melting of ice
B. Evaporation of water
C. Heat of combustion
D. Both (a) and (b)

Answer 1

Hint: If a system undergoes an endothermic process or reaction it is said that heat is absorbed by the system. A spontaneous process is a process which occurs on its own without any external aid.

Complete Step by Step Solution:
We know that spontaneous processes occur on their own.
In these processes, a closed system absorbs energy from its surroundings into the system.
All the spontaneous processes are irreversible.

A. Melting of ice
It is an endothermic process as heat is absorbed by the system from the surrounding.
In this case, the solid-state changes into a liquid state.
This reaction once initiated does not need any exterior help like constant heat supply.
So, this is a spontaneous process.
So, A is correct.

B. Evaporation of water
In this case, the liquid-state changes into a gaseous state.
The entropy of a gas is more than the entropy of a liquid. This is because the degree of disorderness is the highest in a gaseous state due to the availability of free space and the small size of the gaseous particles.
The second law of thermodynamics acknowledges that "a process in an isolated system will be spontaneous if the entropy of the system enhances with time."
So, this is a spontaneous process.
So, B is correct.

C. Heat of combustion
This is an exothermic reaction because heat is released by the system into the surroundings.
So, C is incorrect.
Hence, the melting of ice and evaporation of water both are spontaneous reactions.

So, option D is correct.

Note: The second law of thermodynamics acknowledges that "a process having an isolated system will be spontaneous if the entropy of the system enhances with time."
Entropy is nothing but the degree of disorderness of a system. A higher degree of disorderness will conclude in higher entropy. The entropy of the universe is increasing.