A gaseous system at obeys the equilibrium (at ) Shortly after a disturbance

CHEMISTRY · Multi-part · A Level · Chemistry · Chemical equilibria (Le Chatelier’s principle and Kc) · Chemical equilibria (Le Chatelier’s principle and Kc)

Problem

A gaseous system at 350 K350\,\text{K} obeys the equilibrium 2 A(g)⇌B(g)2\,A(g) \rightleftharpoons B(g)  Kc=0.25K_c = 0.25 (at 350 K350\,\text{K}) Shortly after a disturbance, a researcher records the molar concentrations of A and B at 2 s2\,\text{s} intervals. The data, obtained from a plot that employs a logarithmic (base-10) y-axis, are summarized below.
Time (s)[A] (M)[B] (M)
01.0×10−21.0 \times 10^{-2}2.0×10−52.0 \times 10^{-5}
27.9×10−37.9 \times 10^{-3}3.0×10−53.0 \times 10^{-5}
46.3×10−36.3 \times 10^{-3}4.0×10−54.0 \times 10^{-5}
65.0×10−35.0 \times 10^{-3}5.0×10−55.0 \times 10^{-5}
85.0×10−35.0 \times 10^{-3}6.3×10−56.3 \times 10^{-5}
(a) Calculate the reaction quotient QcQ_c at t=0 st = 0\,\text{s} and predict the initial direction of the net reaction. (b) Compute the reaction quotient QcQ_c at each subsequent time listed. Using these values, identify the earliest time (within the data set) at which the system can reasonably be considered to have reached equilibrium, and justify your choice quantitatively. (c) The researcher chose a logarithmic concentration axis for the original graph. Explain two advantages of a logarithmic scale when tracking the approach to equilibrium for this reaction.

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