The Gibb's function is defined in terms of temperature (T), enthalpy (H), and entropy (S) as G=H−TS In a thermodynamic process with no composition change, change in Gibb's energy is dG=dH−TdS−SdT . . . (i) Using the combined first and second laws dU‌‌=TdS−pdV‌ and ‌dH=TdS+Vdp‌ in (i) gives ‌ dG‌‌=Vdp−SdT