The elementary equilibria below occur in the same reaction vessel at constant temperature
CHEMISTRY · Single correct · A Level · Chemistry · Chemical equilibria (Le Chatelier’s principle and Kc) · Chemical equilibria (Le Chatelier’s principle and Kc)
Problem
The elementary equilibria below occur in the same reaction vessel at constant temperature.
1. A(g)⇌B(g)K1
2. B(g)⇌C(g)K2
Which of the following best explains why the equilibrium constant for A(g)⇌C(g) is equal to K1K2?
(a) Because both steps shift concentrations in the same direction, the numerical values of K1 and K2 must be added to reflect the combined effect.
(b) You must square K1 and then multiply by K2 because B appears in two separate equilibria while A appears only once.
(c) Multiplying the two equilibrium expressions cancels the concentration terms for the intermediate B, leaving only A and C in the overall expression.
(d) The intermediate B accumulates negligibly, so the larger of K1 or K2 alone effectively determines the overall constant.