Isothermal Expansion of an Ideal Gas - Practice Questions & MCQ

Isothermal reversible and irreversible 

Let us consider a cylinder fitted with a frictionless and weightless piston having an area of cross-section as 'A'. If the extemal pressure (P) is applied on this piston and the value of P is slightly less than that of the internal pressure of the gas When the gas undergoes a little expansion and the piston is pushed out by a small distance dx the work done by the gas on the piston is given by as

Isothermal irreversible expansion of an ideal gas

When a gas expands against a constant external  . There is a considerable difference between the gas pressure (inside the cylinder) and the external pressure. The temperature does not change during the process.

Work done in Isothermal reversible expansion of an ideal gas 

As a small amount of work done dW on the reversible expansion of a gas through a small volume dV against an external pressure 'P' can be given as

So the total work done when the gas expands from initial volume V₁ to final volume V₂ is given as

Here negative sign indicates work of expansion and it is generally greater than work in the irreversible process

As in such a case, the temperature is kept constant and internal energy depends only on temperature so it internal energy is constant.

Hence, during isothermal expansion, work is done by the system at the expense of heat absorbed.