The standard free energy changes for conversion of phosphoenol pyruvate (PEP) to pyruvate, and ATP synthesis are shown below.
\[
\text{PEP} + \text{H}_2\text{O} \rightleftharpoons \text{pyruvate} + \text{P}_i \quad \Delta G^\circ = -61.9 \, \text{kJ/mol}
\]
\[
\text{ADP} + \text{P}_i \rightleftharpoons \text{ATP} + \text{H}_2\text{O} \quad \Delta G^\circ = 30.5 \, \text{kJ/mol}
\]
The starting concentrations of PEP, ADP, pyruvate, and ATP are 25, 25, 50, and 50 mM, respectively. The value of the universal gas constant (R) is 8.315 J·mol\(^{-1}\)·K\(^{-1}\). The actual free energy change in kJ·mol\(^{-1}\) for the reaction
\[
\text{PEP} + \text{ADP} \rightarrow \text{pyruvate} + \text{ATP}
\]
carried out at 37°C will be ________ (rounded off to one place of decimal).