Question

Entropy of the universe is:
A. Constant
B. Zero
C. Continuously decreasing
D. Continuously increasing

Answer 1

Hint: Second law of thermodynamics says that entropy of an isolated system can never decrease with respect to time. It can be zero only if the processes are irreversible which is not possible for all processes in the universe combined.

Complete step by step solution:
Entropy is a physical quantity which describes the unavailability of thermal energy a material has for its conversion to mechanical energy. This is also roughly said as a measure of randomness or disorder in the system. Consider a river waterfall. The process of conversion of potential energy to kinetic energy takes place to bring the system in equilibrium with the lower altitude of the fall. This process is irreversible. But there is also loss of some potential energy to other energy forms and thus kinetic energy at the bottom of the cliff will be slightly less than total potential energy difference. This is also measured in entropy. In the process the entropy has increased. Similarly for all the processes in the universe, the total energy expended is to bring the net system in thermal equilibrium and the entropy will continuously increase. This is the second law of thermodynamics which states that entropy of an isolated system can never decrease with respect to time. Thus we can say that option D is correct.

Note: Now entropy will be zero for reversible reactions but no reaction is irreversible. There is always loss of energy in a way which cannot be extracted from the process.