# How do you calculate work for isothermal processes?

The basic premise is constant temperature. For ideal gases, the change in internal energy $U$ is a function of ONLY temperature. From the first law of thermodynamics, we must have:
${\overbrace{\cancel{\Delta U}}}^{\text{0 for } \Delta T = 0} = q + w$
And the work $w$ done by or on the system is equal to the heat flow $q$ into or out from the system, respectively:
$\underline{w = - q}$