A flask is charged with 0.124 mol of A and allowed to react to form B according to the reaction A(g) -B(g). The following data are obtained for [A] as the reaction proceeds:
-The average rate of appearance of B between 20 s and 30 s is mol/s.

Question

A flask is charged with 0.124 mol of A and allowed to react to form B according to the reaction A(g) -B(g). The following data are obtained for [A] as the reaction proceeds: 
-The average rate of appearance of B between 20 s and 30 s is mol/s.

Quizplus · Accepted Answer

To determine the rate of appearance of B between 20 s and 30 s, we need to find the change in concentration of B over that time period, divided by the time interval:
rate = Δ[B]/Δt

Looking at the graph, at 20 s the concentration of B is zero, and at 30 s the concentration of B is 0.066 M. Therefore:
Δ[B] = 0.066 M - 0 M = 0.066 M

Δt = 30 s - 20 s = 10 s

Plugging these values into the rate equation:
rate = 0.066 M / 10 s = 0.0066 M/s

Since we want the average rate of appearance of B, the answer is positive. Therefore, the best choice is B, +1.5 × 10^-2 M/s.

A Flask Is Charged with 0