A sealed flask contains the gaseous reaction at 298 K
CHEMISTRY · Single correct · A Level · Chemistry · Kinetics · Kinetics
Problem
A sealed flask contains the gaseous reaction 2NO2(g)⇌N2O4(g) at 298 K. In the absence of a catalyst, measurable equilibrium concentrations are first obtained after 10 minutes. When a finely divided solid catalyst is introduced and the experiment is repeated at the same temperature and initial pressures, the same equilibrium concentrations are reached in about 1 minute.
Which statement best accounts for this observation?
(a) The catalyst lowers the activation energy for the forward reaction only, so the forward rate increases while the reverse rate is essentially unchanged, leading to faster formation of N2O4 and a shifted equilibrium.
(b) The catalyst selectively adsorbs NO2, effectively reducing its gaseous concentration; by Le Châtelier’s principle the equilibrium is driven toward N2O4.
(c) The catalyst provides an alternative reaction pathway with a lower activation energy, accelerating both the forward and reverse reactions without altering the value of K.
(d) The catalyst stabilizes the products, lowering their Gibbs free energy and thereby increasing the equilibrium constant.