Van't Hoff Isotherm

Van't Hoff Isotherm is a quantitative relation of free energy change accompanying a chemical reaction and it directs the direction of a particular reaction.
Let us consider a chemical reaction-
aA + bB ⇌ cC + dD

where a, b, c and d are the number of moles of A, B, C and D respectively.
We know that free energy per mole is given as-
F = F^o + RT lnP

If the free energy per mole of A, B, C and D be F_A, F_B, F_C and F_D at the respective pressures P_A, P_B, P_C and P_D and their standard free energies be F^o_A, F^o_B, F^o_C and F^o_D. Then-

F_A = F^o_A + RT lnP_A
F_B = F^o_B + RT lnP_B
F_C = F^o_C + RT lnP_C
F_D = F^o_D + RT lnP_D
Now the free energy change of a chemical reaction is given as-
ΔF = ΣΔF_Product − ΣΔF_Reactant
or, ΔF = cF_C + dF_D − aF_A + bF_B

Hence-

This equation is known as Van't Hoff Isotherm.

Related Topics
Van't Hoff Isochore
Van't Hoff Equation