I was reading through Schroeder's Thermal Physics textbook, where I came across the following (in the section on Helmholtz free energy): "If the environment is one of constant temperature, the system can extract heat from this environment for free, so all we need to provide, to create the system from nothing, is any additional work needed."
My question is now: Why can a system extract heat for free when the environment is at constant temperature? Or is this the same as saying dW=-dQ for an isothermal process?