An adiabatic process is one in which :
In thermodynamics, an adiabatic process is one that occurs without transfer of heat or matter between a thermodynamic system and its surroundings.
For a closed system, one may write the first law of thermodynamics thus:
ΔU denotes the change of the system's internal energy,
Q the quantity of energy added to it as heat, and
W the work done on it by its surroundings.
If the system walls are adiabatic (Q = 0), but not rigid (W ≠ 0), then change in internal energy is equal to change in internal energy.