I have read that adiabatic process is isentropic because there is no heat exchange in an adiabatic process and thus no change in entropy.
But my question is - Even in adiabatic process, work can be done. Let's take an example of an adiabatic vessel with a piston attached. That vessel does not exchange heat but work can be done by pulling in or out the piston.
If the volume of the system changes, isn't entropy also changed, even in a reversible adiabatic process?
EDIT : I know that change in entropy is defined as change in heat divided by temperature. Since there is no change in heat in an adiabatic process, the entropy is zero. My question is different - What I see entropy as - It is a measure of the different microstates in which a system can be. So, even if there is no exchange of heat, can't number of thermally achievable microstates increase if we increase the volume by letting the system do volume work? Why is only heat exchange considered as a mechanism for entropy change?