Consider a gas contained in a rigid container of volume 20m3. What will be the change in internal energy if 50J of heat is provided to it? Assume the gas exerts a pressure of 1atm on the walls.

The first law of thermodynamics states that energy can neither be created nor destroyed, only altered in form. For any system, energy transfer is associated with mass crossing the control boundary, external work, or heat transfer across the boundary. These produce a change of stored energy within the control volume.