CHEMISTRY · Multi-part · A Level · Chemistry · Chemical equilibria (Le Chatelier’s principle and Kc) · Chemical equilibria (Le Chatelier’s principle and Kc)
Problem
Reaction E(g) ⇌ F(g) is studied at 298K. The researcher provides a verbal description of the rate-versus-time graph:
• From 0s to 60s: forward rate decreases linearly from 0.200molL−1s−1 to 0.120molL−1s−1; reverse rate increases linearly from 0.000molL−1s−1 to 0.080molL−1s−1.
• From 60s to 120s: both rates change linearly such that forward rate falls from 0.120molL−1s−1 to 0.090molL−1s−1, while reverse rate rises from 0.080molL−1s−1 to 0.090molL−1s−1.
• After 120s: both rates remain constant and equal at 0.090molL−1s−1.
Respond to the prompts below.
(1) Part 1: (a) Construct a clearly labeled sketch of the forward- and reverse-rate curves for 0s≤t≤160s that is consistent with the description provided. (A precise scale is not required, but the relative positions and slopes must be accurate.)
(2) Part 2: (b) Divide the time axis into all distinct regions where the sign of the net rate of formation of F is constant, and state the sign for each region. Explain how you determined the boundaries of each region.
(3) Part 3: (c) Using the slopes reported for 0s≤t≤60s, estimate the change in concentration of E that occurs during this interval. State any assumptions you make.
(4) Part 4: (d) Suppose the initial amount of F in the reactor were doubled while all other conditions remained the same. Predict qualitatively how each of the two rate curves in part (a) would be altered, and discuss whether the time required to reach equilibrium would increase, decrease, or remain unchanged.