Hydrogen iodide decomposes according to the balanced equation 2 HI(g) ⇌ H2(g) + I2(g)…
CHEMISTRY · Multi-part · A Level · Chemistry · Chemical equilibria (Le Chatelier’s principle and Kc) · Chemical equilibria (Le Chatelier’s principle and Kc)
Problem
Hydrogen iodide decomposes according to the balanced equation
2 HI(g) ⇌ H2(g) + I2(g) Kc = 54.3 at 448 °C.
A 1.50 L reaction vessel at this temperature is filled with a gaseous mixture containing [HI] = 0.0100 M, [H2] = 0.0600 M, and [I2] = 0.0400 M.
(a) Compute the value of the reaction quotient Q for the initial mixture and predict the direction in which the system must proceed to attain equilibrium.
(b) Identify which component is present in the smallest stoichiometric excess relative to the balanced equation, and explain how this affects the algebraic setup of the subsequent equilibrium calculation.
(c) Introduce a single symbol to represent the change in concentration that occurs as the system approaches equilibrium. Write expressions for the equilibrium concentrations of all species in terms of that symbol, taking into account the stoichiometry and your conclusion from part (b).
(d) Generate and solve the numeric equation that results when the expressions from part (c) are substituted into the equilibrium‐constant expression. Provide the equilibrium concentration of each species to the correct number of significant figures.
(e) Demonstrate that the calculated values satisfy both mass balance and the equilibrium‐constant expression within reasonable numerical tolerance.