A system at contains gaseous reactants G and H in the reversible reaction
CHEMISTRY · Multi-part · A Level · Chemistry · Chemical equilibria (Le Chatelier’s principle and Kc) · Chemical equilibria (Le Chatelier’s principle and Kc)
Problem
A system at 350K contains gaseous reactants G and H in the reversible reaction G⇌H. The reaction is allowed to proceed until equilibrium is established at 420s, where both forward and reverse rates are 0.025molL−1s−1. At t=500s, an additional pulse of H is rapidly injected, instantaneously raising the reverse rate to 0.065molL−1s−1, while the forward rate remains at 0.025molL−1s−1. Over the next several minutes, the two rates evolve smoothly and eventually coincide again at 0.035molL−1s−1.
Using this information, address the following tasks.
(1) Part 1: (a) Immediately after the injection at t=500s, state the direction of the net chemical change and quantify the initial net rate.
(2) Part 2: (b) Explain, with reference to collision-level reasoning, why the reverse rate increased instantaneously while the forward rate did not.
(3) Part 3: (c) Describe qualitatively how each rate curve (forward and reverse) must change after t=500s to satisfy both kinetic and equilibrium considerations, and indicate the new equilibrium rate value.
(4) Part 4: (d) Construct a reasoned argument to determine whether the equilibrium constant K for G⇌H at 350K is affected by the injection of additional H. Your answer should integrate kinetic and thermodynamic perspectives.
(5) Part 5: (e) Suppose the experiment is repeated at 375K. Predict how the final equilibrium rate (the value where the two curves coincide) would compare with 0.035molL−1s−1 and justify your prediction.