Chapter 8: Multiple Reactions

Concentration-Time Trajectories

1. The following concentration-time trajectories were observed in a batch reactor

A graph with concentration (Ci) on the y-axis and time (t) on the x-axis, showing four curves labeled A, B, C, and D. Curve A starts high and decreases over time. Curve B starts low and increases. Curve C has a peak in the middle before decreasing. Curve D increases steadily.

Which of the following reaction pathways best describes the data:

a) \( A \rightarrow B \rightarrow C \rightarrow D \)

b) \( A \rightarrow B \)
\( A \rightarrow C \rightarrow D \)

c) \( A \rightarrow B \rightarrow C \rightarrow D \)
\( A \rightarrow D \)

Solution

2. Sketch the concentration-time trajectory for the reaction:

1) \( A + B \rightarrow C \)

2) \( B + C \rightarrow D \)

\( C_{A0} = 4 \ \text{mol/dm}^3 , \quad C_{B0} = 6 \ \text{mol/dm}^3 , \quad C_{C0} = C_{D0} = 0 \)

A blank graph with concentration (Ci) labeled on the y-axis and time (t) labeled on the x-axis. No data or curves are present.

Solution

Solution: Part 1

Choice B is the answer. Choices A and C are incorrect because they show species B eventually consumed, which is clearly not the case.

Back to Problem 1

Problem 2

Solution: Part 2

A graph labeled 'Self Test' with concentration on the y-axis and volume (V) on the x-axis. It contains four curves labeled C_A (blue), C_B (green), C_C (cyan), and C_D (red). C_A and C_B decrease over time, C_C increases and then plateaus, and C_D steadily increases. A legend in the upper right corner identifies the colors corresponding to each concentration.

(1) B virtually consumed so no more D can be produced in reaction 2.

(2) Rates of Consumption of A and Ba are virtually the same.

(3) Rate of consumption of B greater than that of A owing to Reaction 2.

Below is the polymath code typed in to produce the graph above.

Back to Problem 2

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