Can Isothermal Process Be Zero?

But for the vaporization of liquid (which is an isothermal process) it is not zero. But in the case of liquid vaporization (e.g. liquid water to steam) (boiling at constant temperature), the internal energy change is not zero. ...

Is work 0 in an isothermal process?

In Isothermal process the temperature is constant. The internal energy is a state function dependent on temperature. Hence, the internal energy change is zero. For the process you are describing the work is done by the system, but had you not supplied heat, then the temperature would have dropped.

Is Delta U zero for isothermal?

Delta U is equal to zero for an ideal-gas isothermal-expansion (reversible or irreversible) because for an ideal gas U = 3/2 nRT. That is, if the moles of gas stay the same n is constant, R is the gas constant, and if T is constant (which is what isothermal means) then U is constant which means delta U = 0.