CHEMISTRY · Multi-part · A Level · Chemistry · Chemical equilibria (Le Chatelier’s principle and Kc) · Chemical equilibria (Le Chatelier’s principle and Kc)
Problem
In a sealed container, the reversible decomposition reaction
X2(g)⇌2X(g)
is allowed to reach equilibrium at a fixed temperature for which the equilibrium constant Kc=4.0.
Three particulate diagrams (labeled A, B, and C) are described below. Each diagram shows a total of 40 gas particles of two types:
• black dimers represent X2 molecules
• white monomers represent X atoms
Diagram A: 20 dimers and 0 monomers
Diagram B: 8 dimers and 24 monomers
Diagram C: 4 dimers and 32 monomers
Assume the volume of the container is the same in all cases so that molar concentrations are directly proportional to the particle counts.
(a) Derive the numerical value of the ratio [X2][X]2 that corresponds to Kc for this reaction.
(b) Using the particle counts provided, calculate the value of the ratio [X2][X]2 for each diagram.
(c) Identify which diagram most accurately represents a system at equilibrium at the stated temperature, and justify your choice quantitatively.
(d) Explain, in terms of the relative abundance of reactant and product species, how the magnitude of Kc=4.0 is reflected in your selected diagram.