Practice problems - Rates of Reaction

Question

2. In the reaction A + 2 B → 3 C + 4 D, the initial concentration of B was 0.0443 M after 17.3 min the concentration of B was 0.0305 M. What is the average rate of disappearance (M/s) of reactant A?

3. In the reaction A + 2 B → 3 C + 4 D, the initial concentration of B was 0.0389 M after 11.9 min the concentration of B was 0.0222 M. What is the average rate of appearance (M/s) of reactant C?

4. In the reaction A + 2 B → 3 C + 4 D, the initial concentration of A was 0.0351 M after 18.3 min the concentration of A was 0.0199 M. What is the average rate of disappearance (M/s) of reactant B?

Answer 1

(2). A + 2B => 3C + 4D

rate disappearance of B = 0.0305 - 0.0443 / 17.3 min = -0.000798 M / min

rate of disappearance of A will be 1/2 that of B based on the stoichiometric coefficients in the balanced equation, so

rate of disappearance of A = -0.000798 / 2 = -0.000399 M / min = 6.65x10^-6 M/s

(3). A + 2B => 3C + 4D

rate of disappearance of B = 0.0222 - 0.0389 / 11.9 min = -0.00140 M / min

rate of appearance of C will be 1.5 times (3/2) that the disappearance of B based on the stoichiometric coefficients of the balanced equation.

Rate of appearance of C = +0.00140 (3/2) = 0.00211 M / min = 3.51x10^-5 M/s

(4). A + 2B => 3C + 4D

rate of disappearance of A = 0.0199 - 0.0351 / 18.3 min = 0.000831 M / min

Rate of disappearance of B will be twice that (2x) the rate for A based on the stoichiometric coefficients in the balanced equation.

Rate of disappearance of B = 2 x 0.000831 = 0.00166 M / min = 2.77x10^-5 M/s