For three single-step gas-phase reactions carried out at 298 K, the potential energies (in kJ mol⁻¹) of the reactants, transition states, and products are listed in the table below. The reactants of every reaction are assigned a reference energy of 0 kJ mol⁻¹.
Reaction
Transition-state energy (kJ mol⁻¹)
Product energy (kJ mol⁻¹)
A
+90
–60
B
+55
–20
C
+110
+30
Answer the following.
(a) For each reaction, calculate the enthalpy change ΔH in kJ mol⁻¹. Clearly indicate the sign of ΔH for every reaction.
(b) For each reaction, determine the activation energy Ea in kJ mol⁻¹.
(c) Rank the three reactions in order of increasing thermodynamic favorability. Justify your ranking with reference to the calculated values.
(d) Rank the three reactions in order of increasing expected rate at 298 K, assuming that all three reactions have comparable collision frequencies. Justify your ranking.