Answer the following questions
Calculate the standard free energy change for the following reaction at $$ 25^{\circ}\,C $$.
$$ Au(s) + Ca^{2+} (1 \, M) \rightarrow Au^{3+}(1\,M) + Ca(s) $$
$$ E^{o}_{Au^{3+} / Au} = + 1.50 \,V , E^{o}_{Ca^{2+} / Ca} = - 2.87\,V $$
Predict whether the reaction will be spontaneous or not at $$ 25^{\circ}\,C $$ . Which of the above two half cells will act as an oxidizing agent and which one will be a reducing agent ?