A reversible gaseous reaction C ⇌ D is carried out in a constant-volume reactor at
CHEMISTRY · Multi-part · A Level · Chemistry · Chemical equilibria (Le Chatelier’s principle and Kc) · Chemical equilibria (Le Chatelier’s principle and Kc)
Problem
A reversible gaseous reaction C ⇌ D is carried out in a constant-volume reactor at 330K. The rates of the forward and reverse reactions are monitored for 600 s and displayed as two smooth curves on a rate-versus-time plot. Numerical readings taken every 100 s are summarized below.
Time (s): 0 100 200 300 400 500 600
Forward rate (molL−1s−1): 0.150 0.095 0.070 0.055 0.045 0.042 0.041
Reverse rate (molL−1s−1): 0.000 0.030 0.050 0.055 0.060 0.063 0.064
Answer the questions that follow.
(1) Part 1: (a) Using an appropriate method, estimate to the nearest 10 s the time at which equilibrium is first achieved. Show your reasoning clearly.
(2) Part 2: (b) For the interval between 0 s and the time you identified in part (a), calculate the average net rate of conversion of C to D. Clearly indicate all steps and assumptions.
(3) Part 3: (c) The experimental uncertainty in each rate measurement is ±0.003 molL−1s−1. Discuss whether this uncertainty affects your conclusion in part (a), and support your answer with quantitative reasoning.
(4) Part 4: (d) Based solely on the rate data provided, predict whether the concentration of C at t = 600 s is greater than, less than, or equal to its concentration at t = 400 s. Justify your prediction.