Question

in a reversible process it is said that the systemand the surroundings should be in thermodynamical equilibrium which includes mechanical equilibrium. so how does work take place in a situation where there is mechanical equilibrium

Answer 1

Dear Student,
A reversible process is the one in which the system and surroundings are in thermodynamical equlibrium. A reversible takes place infinitesimally slowly and can be reversed back to the original state.
A system in thermal equlibrium will also have mechanical equilibrium. For a system to have mechanical equilibrium the internal energy should be zero . Internal energy or the intrinsic energy is the sum of molecular kinetic and potential energy of the substance under a given set of conditions.
In mechanical equilibrium the pressure change is zero and internal energy is zero but still work will be done by heat absorbed by the system.
Regards!