At 600 K, the decomposition of dinitrogen tetroxide proceeds according to the…
CHEMISTRY · Multi-part · A Level · Chemistry · Chemical equilibria (Le Chatelier’s principle and Kc) · Chemical equilibria (Le Chatelier’s principle and Kc)
Problem
At 600 K, the decomposition of dinitrogen tetroxide proceeds according to the balanced chemical equation
N2O4(g)⇌2NO2(g)
with an experimentally determined equilibrium constant Kc=4.6×102. A chemistry student proposes three different manipulations of this equilibrium expression:
• Step I: Reverse the reaction so that nitrogen dioxide dimerizes to form dinitrogen tetroxide.
• Step II: Multiply every stoichiometric coefficient in the original reaction by two.
• Step III: First perform Step I, then perform Step II on the reversed reaction.
Respond to the following prompts.
(a) Qualitatively predict how the magnitude of the equilibrium constant obtained in Step I compares with 4.6×102. Justify your prediction without performing a numerical calculation.
(b) Determine, in terms of Kc, the numerical expression for the equilibrium constant that results from Step II. Explain your reasoning.
(c) Derive an algebraic expression, in terms of Kc, for the equilibrium constant that would correspond to the overall reaction produced by Step III. Provide a clear verbal justification for each algebraic operation used.
(d) Explain how the physical interpretation of a “large” versus a “small” equilibrium constant changes when a reaction is written in the forward versus the reverse direction. Relate your explanation to the specific transformations carried out in Steps I–III.