A mixture of gases at 350 K undergoes the reversible reaction E(g) ⇌ F(g) + G(g) 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 mixture of gases at 350 K undergoes the reversible reaction
E(g) ⇌ F(g) + G(g)
At t=0 the system is at equilibrium. Suddenly, additional E is injected, instantaneously raising the partial pressure of E by 0.250 atm. The forward and reverse rates are then monitored at the times shown.
Time after injection / s
Rate_forward / (atms−1)
Rate_reverse / (atms−1)
pE / atm
0
0.00
0.00
pEeq+0.250
5
0.036
0.012
—
10
0.029
0.017
—
20
0.022
0.020
—
40
0.019
0.019
—
80
0.019
0.019
pEnew eq
(The dashes indicate that the partial pressure of E was not directly measured at those times.)
(1) Using the rate data, explain qualitatively how the system responds to the sudden increase in pE during the first 40 s.
(2) Account for the observation that the forward and reverse rates are equal again at 40 s even though pE has not yet been reported as constant.
(3) Design an experimental method (other than rate measurement) that could verify the attainment of the new equilibrium by 80 s. Describe the measurable quantity and the criterion you would use.
(4) If the temperature were raised while keeping total pressure constant after 80 s, predict, with justification based on kinetic principles, how both the forward and reverse rates would immediately change.