Question 785: Thermodynamics & KTG

Question

Select the WRONG statement from the following. For an isothermal process

Accepted Answer

Option C is the incorrect statement for an isothermal process. An isothermal process is one in which the temperature (T) of a system remains constant throughout the process. In thermodynamics, the equation of state for an ideal gas is given by the ideal gas law, which states:
$ PV = nRT $
where P is the pressure, V is the volume, n is the number of moles of gas, R is the universal gas constant, and T is the temperature.
In an isothermal process, because the temperature T is constant, the product of P and V must also remain constant for a given amount of gas with a fixed number of moles (n). This is because R is a constant and T is held constant in the process, and thus, the product PV does not change even as pressure and volume do. Therefore,
$ PV = constant $
This directly contradicts Option C, which states that the equation of state PV is not constant. Since in an isothermal process for an ideal gas, PV always remains constant if the temperature is constant, Option C is the wrong statement.
Let's verify the other options for an ideal gas undergoing an isothermal process:
Option A is correct because in an isothermal expansion or compression, the energy exchanged with the surroundings is indeed used to do work. No change in internal energy occurs (Option D), due to the fact that internal energy for an ideal gas is a function of temperature alone, and in an isothermal process, temperature does not change. The energy needed to change the volume of the gas comes from or goes into the work done by or on the gas.
Option B is a somewhat ambiguous statement. It can be interpreted as saying the system is in a state of thermal equilibrium with the environment because the temperature remains constant. However, maintaining a perfect thermal equilibrium throughout the process would mean the surroundings are also at the same temperature and capable of supplying or absorbing energy without changing temperature themselves, which is a theoretical idealization.
Nevertheless, Option C is clearly the wrong statement out of the four provided when considering the definition and properties of an isothermal process.

Answer

Energy exchanged is used to do work

Answer

Perfect thermal equilibrium with environment

Answer

Equation of state PV is not constant.

Answer

No change internal energy.

Thermodynamics & KTG

Select the WRONG statement from the following. For an isothermal process

Choose the correct answer: