The change in entropy of a closed system is always positive. The change in entropy of an open system can be negative with the action of the other system, but then the change in entropy of the other system is positive and the total change in entropy of these systems is positive too.

Can entropy be negative?

The true entropy can never be negative. By Boltzmann's relation S = k ln OMEGA it can be at minimum zero, if OMEGA, the number of accessible microstates or quantum states, is one. However, many tables arbitrarily assign a zero value for the entropy corresponding to, for example, a given temperature such as 0 degrees C.

Why is entropy always positive?

There is no net shift in entropy if a reversible mechanism occurs. ... Entropy often increases in an irreversible process, so the change in entropy is optimistic. There is a constant rise in the overall entropy of the universe.