Answer to Question #66324 in General Chemistry for Carley

Question

For the following chemical reaction:

This is an image of a chemical equation. A + B, reaction arrow, C.

Three students measure the initial reaction rate, but under different conditions (initial concentration of substances A and B).

Student
[A] [B]
1 0.20 M 0.20M
2 0.20 M 0.40M
3 0.40 M 0.40M

The rate constant for this reaction, at a certain temperature, is 2.5 M-1s-1 (assume it is first order with respect to both reactants):

a.Which student observed the reaction which proceeded the quickest?
b.What is the rate of the quickest reaction?
c.What is the rate of the slowest reaction?
d.Does the rate of reaction remain constant for the duration of the reaction? Briefly explain your answer.
e.Give an explanation as to why each student would obtain different experimental results for the initial reaction rate.

Answer 1

1. V = k x [A] x [B] = 2.5 x 0.2 x 0.2 = 0.1 Mxs -1

2. V = k x [A] x [B] = 2.5 x0.2 x 0.4 = 0.2 Mxs -1

3. V = k x [A] x [B] = 2.5 x0.4 x 0.4 = 0.4 Mxs -1

a. The third student observed the reaction which proceeded the quickest

b. V = 0.4 Mxs -1

c. V = 0.1 Mxs -1

d. No, the reaction rate doesn't remain constant during the duration of the reaction, because the concentrations of reactants decrease during the process. The rate decreases with concentration decreasing.

e. Because initial reaction rate depends on initial concentration of substances A and B, they are all different