A chemist studies the gas-phase conversion of molecule X to molecule Y
CHEMISTRY · Multi-part · AP · Chemistry · Thermodynamics and Electrochemistry · Thermodynamics and Electrochemistry
Problem
A chemist studies the gas-phase conversion of molecule X to molecule Y. At 298 K she measures the following energetic information for the uncatalyzed process:
• The energy of the transition state is 175 kJ mol⁻¹ above the reactants.
• The products are 45 kJ mol⁻¹ lower in Gibbs free energy than the reactants.
Assume all quantities refer to standard-state Gibbs free energies at 298 K.
(a) Identify the numerical value of the activation energy for this reaction and explain, in words, what physical meaning this quantity has in the context of molecular collisions.
(b) Calculate the standard free-energy change, ΔG298∘, for the reaction. State whether the reaction is thermodynamically favored and justify your answer.
(c) Despite the value found in part (b), the chemist observes essentially no formation of Y over several hours at 298 K. Using the information provided, explain why the reaction mixture is said to be under kinetic control.
(d) Propose one specific experimental modification that would increase the rate of formation of Y without changing its thermodynamic favorability. Justify how your modification addresses the factor discussed in part (a).