A proposed mechanism for the conversion of to involves three elementary steps

CHEMISTRY · Multi-part · AP · Chemistry · Kinetics · Kinetics

Problem

A proposed mechanism for the conversion of EE to GG involves three elementary steps. Step 1 E⇌FE \rightleftharpoons F Ea1=50 kJ mol−1E_{a1} = 50\,\text{kJ mol}^{-1} ΔH1=+15 kJ mol−1\Delta H_1 = +15\,\text{kJ mol}^{-1} Step 2 F→HF \to H Ea2=35 kJ mol−1E_{a2} = 35\,\text{kJ mol}^{-1} ΔH2=−20 kJ mol−1\Delta H_2 = -20\,\text{kJ mol}^{-1} Step 3 H→GH \to G Ea3=60 kJ mol−1E_{a3} = 60\,\text{kJ mol}^{-1} ΔH3=−40 kJ mol−1\Delta H_3 = -40\,\text{kJ mol}^{-1} The potential energy of EE is defined as 0 kJ mol−10\,\text{kJ mol}^{-1}. (a) Construct a qualitative reaction-coordinate diagram for the overall process E→GE \to G, accurately reflecting the given numerical data. Label all intermediates, transition states, activation energies, and enthalpy changes. (b) Determine which species (EE, FF, HH, or GG) is thermodynamically most stable. Justify your choice using the diagram or numerical values. (c) Identify the rate-determining step for the uncatalyzed mechanism and explain your reasoning in terms of activation energies. (d) A chemist proposes adding a catalyst that selectively lowers Ea3E_{a3} to 25 kJ mol−125\,\text{kJ mol}^{-1} without affecting the other steps. Redraw only the portion of the energy profile that would change and predict qualitatively how this catalyst would influence (i) the overall rate law and (ii) the relative concentrations of intermediates FF and HH at steady state.

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