CHEMISTRY · Single correct · A Level · Chemistry · Chemical equilibria (Le Chatelier’s principle and Kc) · Chemical equilibria (Le Chatelier’s principle and Kc)
Problem
In an experiment, the forward rate for a gas-phase reversible reaction decreases linearly from 1.0 mol L⁻¹ s⁻¹ at t=0 to 0.20 mol L⁻¹ s⁻¹ at t=50 s. Over the same interval, the reverse rate increases linearly from 0.05 mol L⁻¹ s⁻¹ to 0.20 mol L⁻¹ s⁻¹.
Between t=0 s and t=50 s, which statement most accurately characterizes the net chemical change in the system?
(a) No net chemical change occurs at any time during the 50\,s because the forward and reverse rates have the same initial--final average value.
(b) The system reaches equilibrium at about 25\,s; after that, products are converted back to reactants because the reverse rate rises more quickly than the forward rate.
(c) Reactants are continuously converted to products throughout the 50\,s because the forward rate remains greater than the reverse rate until they become equal at 50\,s.
(d) Equal forward and reverse rates at 50\,s mean equal amounts of reactants and products, so no overall conversion has taken place during the experiment.