In isothermal process ΔU=0. But I am having trouble understanding it.
Say we have an ideal gas, and say my temperature is constant but I move the pressure, volume from (P,V)→(P−dP,V+dV). So the volume has expanded and system has done some work to the surrounding. So my work is non-zero.
So how come ΔU=0? I am really confused here.