A student claims that because balanced forces result in no motion for a book on a table
CHEMISTRY · Single correct · A Level · Chemistry · Chemical equilibria (Le Chatelier’s principle and Kc) · Chemical equilibria (Le Chatelier’s principle and Kc)
Problem
A student claims that because balanced forces result in no motion for a book on a table, balanced forward and reverse rates in a chemical reaction should cause all molecular motion to stop. Which of the following provides the best explanation of why molecular motion persists at chemical equilibrium even though macroscopic properties remain constant?
(a) Because the concentrations of reactants and products become equal at equilibrium, there is no driving force for molecules to collide, so motion ceases.
(b) Since the standard free-energy change ΔG∘ is zero at equilibrium, the system lacks the energy needed for molecular motion.
(c) Molecules retain thermal kinetic energy supplied by the temperature, so collisions continue even though the net reaction progress is zero.
(d) The forward and reverse activation energies exactly cancel at equilibrium, preventing any collisions from having enough energy to proceed.