Question

For the following questions, use the reaction SO3(g) --> SO2(g) + 0.5O2(g), with ΔH = 98.4 kJ/mol and ΔS = 95.64 J/(mol·K). What is the Gibbs free energy of the reaction at 27°C? Is the reaction spontaneous or nonspontaneous at 27°C?

Answer 1

To find the Gibbs free energy of the reaction use the following formula:

`\Delta G=\Delta H-T\Delta S`

Where ΔG is the Gibbs free energy, ΔH is the enthalpy of reaction, ΔS is the reaction entropy and T is the absolute temperature.

Convert the given temperature to kelvin and then replace for the known values to find ΔG:

`\begin{gathered} T=27+273.15=300.15 \\ \Delta G=98.4kJ/mol-(300K)\cdot95.64J/mol \\ \Delta G=98.4kJ/mol-28692J/mol \\ \Delta G=98.4kJ/mol-28.692kJ/mol \\ \Delta G=69.708kJ/mol \end{gathered}`

It means that the Gibbs free energy is 69.708kJ/mol.

According to this value (that is greater than 0) the reaction is not spontaneous at 27°C.