Praxis Study Companion – Physics (5266) Practice Test

Isochoric means the volume does not change. The crucial point is that work by a gas is given by W = ∫ P dV, so if the volume doesn’t change (dV = 0), the work done is zero. That’s why the statement “Volume constant; gas does no work” is true.

In this situation, pressure can change with temperature. For an ideal gas at constant volume, P = nRT / V, so heating raises the temperature and the pressure, but there’s no expansion or compression to do work. If you add heat at fixed volume, that energy goes into increasing the internal energy (and temperature) rather than doing work.

The other possibilities describe different processes: constant pressure would involve volume change (isobaric), constant temperature would be isothermal, and heat added doing work implies volume change as the gas expands or compresses.