Question

Energy flows out of the system in form of a heat in an internally reversible process. What happened to he entropy of the system? Explain

Answer 1

For a reversible process, the overall change in entropy is zero (i.e. no entropy is created). However, entropy can be transferred between different systems and the environment through reversible processes.

For a system transferring heat/work to/from its environment - as I understand it, for an internally reversible process, no irreversibilities exist within the system. This typically means that the system changes very slowly, without friction, through a series of equilibrium states. Internally reversible process means that there is no 'entropy generation' 'within' the system (eg frictionless system). Conversely, internal irreversibilities occur due to friction or a system moving through non-equilibrium states. Entropy change is zero for such process.

A process is called "internally reversible" if no irreversibility occur within the
boundaries of the system during the process. The paths of the forward and reverse processes coincide for an internally reversible process
A reversible process also termed as Total reversible is defined as a process that can be reversed without leaving any trace on either system or surroundings. This is possible if the net work and heat is 0 for the combined process.

Internally Reversible Isothermal Heat Transfer Processes .Recall that isothermal heat transfer processes are internally reversible:

This equation is particularly useful for determining the entropy changes of thermal energy reservoirs that can adsorb or supply heat indefinitely at a constant temperature.

Entropy transfer to a system increases the entropy of a system where as heat transfer from a system decreases it. In fact loosing heat is the only way the entropy of system can be decreased. The Overall entropy of Internally reversible process is zero.

Externally reversible process means that the heat interaction between the system and the surroundings is taking place through infinitesimally small temperature difference. Hence, increase in entropy of system due to heat gain exactly equals the decrease in entropy of surroundings due to heat loss, thus making the overall change in entropy zero.