Write first law of thermodynamics for isothermal process in an ideal gas.

Explanation

In an isothermal process of an ideal gas, temperature remains constant.
`therefore DeltaU=0`
From first law of thermodynamics,
`DeltaQ-DeltaW=DeltaU` , here `DeltaU=0`
`therefore DeltaQ=DeltaW`
i.e. heat supplied in an isothermal process is used entirely to do work against the surrounding means, it is equal to work done by the system.