Question

Entropy of an adiabatic reversible process is:
A. Positive
B. Zero
C. Negative
D. Constant

Answer 1

Hint: Adiabatic process occurs without the transfer of mass or heat between a thermodynamic system and its surroundings. It is found that this process transfers energy to the surroundings only as work. Adiabatic processes can be reversible or irreversible. The entropy change depends on the heat exchange of the adiabatic system.

Complete step by step solution:
- Entropy change is represented by $\Delta S$
- From second law of thermodynamics, we know that
\[\Delta S=\dfrac{{{q}_{rev}}}{T}\]
Here T=temperature
          \[{{q}_{rev}}\]= heat
Whenever adiabatic process occurs, in this case the heat released q=0, that is there is no heat change doesn’t take place. This means that in this case entropy =
\[\begin{align}
  & \Delta S=\dfrac{0}{T} \\
 & \Delta S=0 \\
\end{align}\]

Hence, we can say that the correct option is (B), that is the entropy of an adiabatic reversible process is zero.

Additional information:
- There are several conditions for the adiabatic process to take place like:
- It is found that the process must be carried out fast so that there is sufficient time available for heat transfer.
- System must be perfectly insulated from the surrounding.
- It is also found that in the adiabatic process the work done is due to the change in its internal energy.
- There is no heat transfer takes place and the temperature also cannot be varied.

 Note: - Reversible adiabatic process is also called as an Isentropic process. In this work transfers of the system are found to be frictionless, there is no transfer of matter or of heat and the process is reversible.
- We should note the difference between the adiabatic process and isothermal process. The adiabatic process occurs without any heat transfer between the surrounding and system. Whereas, the isothermal process occurs at a constant temperature.