23.4.2—Calculations: the equation ΔG

Substitute ΔH° and TΔS° into ΔG° = ΔH° − TΔS°. Convert entropy from J K⁻¹ mol⁻¹ to kJ K⁻¹ mol⁻¹ when enthalpy is in kJ mol⁻¹.

Write the units beside each term and keep the sign of ΔS. Round only after the final calculation, then state what the sign means.

If ΔH° = 40 kJ mol⁻¹, ΔS° = 100 J K⁻¹ mol⁻¹ and T = 298 K, TΔS° = 29.8 kJ mol⁻¹ and ΔG° = +10.2 kJ mol⁻¹.

A negative entropy value makes −TΔS positive; do not drop that double sign.