Four reactions (W, X, Y, and Z) occur in the same solution at 298 K. Their single-step energy profiles are summarized below. All reactant energies are referenced to 0 kJ mol⁻¹.
Reaction
Transition-state energy (kJ mol⁻¹)
Product energy (kJ mol⁻¹)
W
+40
–25
X
+120
–90
Y
+35
+50
Z
+65
+15
A researcher wishes to design a coupled process in which one of the above reactions drives another that is thermodynamically unfavorable.
Answer the following questions.
(a) Identify all reactions in the table that are thermodynamically unfavorable at 298 K. Justify each choice quantitatively.
(b) Select a pair of reactions from the table that could be coupled so that the overall combined process is exothermic. Show the calculation that supports your selection.
(c) For the coupled process you selected in part (b), determine which individual reaction is expected to limit the overall rate. Justify using the numerical data provided.
(d) Propose one practical strategy, other than changing temperature, that could be employed to increase the rate of the rate-limiting reaction identified in part (c). Explain how this strategy relates to features of the energy diagram.