Question

In an isothermal expansion of an ideal gas, select wrong statement :

• A. There is no change in the temperature of the gas
• B. There is no change in the internal energy of the gas
• C. The work done by the gas is equal to the heat supplied to the gas
• D. The work done by the gas in equal to the change in its internal energy

Answer 1

Answer: (D)

The work done by the gas in equal to the change in its internal energy

Answer 2

In an isothermal process, the temperature remains constant, meaning ΔT = 0. For an ideal gas, internal energy (U) depends solely on temperature. Thus, with no temperature change, there is no change in internal energy (ΔU = 0).

The First Law of Thermodynamics states ΔU = Q - W, where Q is heat supplied and W is work done by the system. Since ΔU = 0, Q = W, indicating the heat supplied equals the work done.

The incorrect statement claims the work done equals the change in internal energy (W = ΔU). However, since ΔU = 0 in an isothermal process, this would imply W = 0, which is false for an isothermal expansion where the gas performs positive work. Therefore, the statement "The work done by the gas is equal to the change in its internal energy" is wrong.