For an isothermal process net work done by a system is given by
For an isothermal process net work done by a system is given by
Decrease in Helmholtz free energy
Decrease in Gibbs free energy
Decrease in internal energy
Decrease in heat enthalpy
Solution
Helmholtz free energy change $\Delta A$ represents network done.
As, $dU = dE + dW = TdS - PdV = d(TS) - SdT - PdV$
$d(U-Ts) = -SdT - PdV = dA$
At constant temperature & volume $dA = 0$
For equilibrium for any spontaneous process, the change in Helmholtz free energy $\delta A$ must be negative
i.e. $A_f \leq A_i$ & for an isothermal process
$dA = -PdV$ i.e. $\delta A = -W$