At 25 °C the equilibrium constant for the reaction I2(aq) + I−(aq) ⇌ I3−(aq) is
CHEMISTRY · Multi-part · A Level · Chemistry · Chemical equilibria (Le Chatelier’s principle and Kc) · Chemical equilibria (Le Chatelier’s principle and Kc)
Problem
At 25 °C the equilibrium constant for the reaction
I2(aq) + I−(aq) ⇌ I3−(aq)
is K=700. A chemist prepares 250 mL of a solution that is initially 0.010 M in I2, 0.020 M in I−, and contains no I3−. The solution is then diluted by adding enough water to double the volume to 500 mL while maintaining the temperature.
(a) Calculate the initial molar concentrations of I2 and I− immediately after the dilution but before the reaction has responded.
(b) Determine the value of the reaction quotient, Q, immediately after dilution. Show your work.
(c) Indicate the direction in which the system will proceed to reach equilibrium, based on a comparison of Q and K. Briefly explain your reasoning.
(d) Using an appropriate quantitative method, calculate the equilibrium molar concentrations of I2, I−, and I3− after the system re-establishes equilibrium in the diluted solution. Provide all steps of your calculation and state any assumptions.