Question

If heat is supplied to an ideal gas in an isothermal process,

• A. the internal energy of the gas will increase.
• B. the gas will do positive work.
• C. the gas will do negative work.
• D. the said process is not possible.

Answer 1

The correct option is B the gas will do positive work.

In Isothermal process the temperature is constant.

The internal energy is a state function dependent on temperature. Hence, the internal energy change is zero.

An ideal gas by definition has no interactions between particles, no intermolecular forces, so pressre change at constant temperature does not change internal energy.

Real gases have intermolecular interactions, attractions between molecules at low pressure and repulsion at high pressure. Their internal energy changes with change in pressure, even if temperature is constant.

For an ideal gas, in an isothermal process, ΔU=0=Q−W, so Q=W

Hence gas will do positive work