A gas-phase reaction between substances A and B to form product C was investigated at 298 K. The following kinetic data were obtained:
• Activation energy for the forward reaction, Eaf = 75 kJ mol−1
• Activation energy for the reverse reaction, Ear = 20 kJ mol−1
Energy (kJ) versus reaction progress is the coordinate system assumed for any diagrams you construct.
(a) Calculate the enthalpy change ΔH for the reaction A + B → C. Clearly indicate sign and units.
(b) Using the numerical values of Eaf, Ear, and ΔH, construct a quantitatively scaled potential-energy diagram on axes of your own design. Include numerical energy values on the vertical axis and label reactants, products, transition state, Eaf, Ear, and ΔH.
(c) From your diagram, determine whether the reaction is thermodynamically favored at 298 K and justify your answer using the calculated ΔH.
(d) If a different experiment at the same temperature found Eaf to be 65 kJ mol−1 while Ear remained 20 kJ mol−1, determine the new value of ΔH and state whether the reaction would be more or less exothermic than before.