Question

Which is the correct result according to the second law of thermodynamics?

(a) Total change in entropy is always zero

(b) Total change in entropy in a reversible process is always zero

(c) Total change in entropy in an irreversible process is always zero

(d) Total change in entropy for an irreversible process is negative

I have been asked this question during an online interview.

My doubt stems from A Brief Review of Thermodynamics in division Compressible Flow – Preliminary Aspects of Aerodynamics

Answer 1

Right option is (b) Total change in entropy in a reversible process is always zero

Explanation: In an irreversible process, entropy is generated. This means the change in entropy for an irreversible process is positive. Also, for a reversible process, change in entropy is zero since the entropy is conserved in the universe. Thus, the change in total entropy for an irreversible process is greater or equal to zero while that for the reversible process is zero.