Question

For the following reaction: CH_3 OH(aq) + H^+ (aq) + Cl^- (aq) rightarrow CH_3Cl(aq) + H_2O(l) the value of [H^+] was measured over a period of time. Given the data, find the average rate of disappearance of H^+(aq) for the time interval between each measurement. What is the average rate of appearance of CH_3 CI(aq) for the same time intervals?

Answer 1

The reaction:

CH₃OH (aq) + H⁺ + Cl^- --------------------> CH₃Cl (aq) + H₂O (l)

Rate of disapperance of H⁺ is given by - d[H⁺]/dt

Calculating the same in each intervals of time:

0 to 30 s : Rate = - (2.18 M-2.40 M) / (30 s -0) = 0.0073 M/s

30s to 58s : = - (2.06 M-2.18 M) / (58 s - 30 s) = 0.0042 M/s

58s to 124s: = - (1.89 M - 2.06 M) / (124 s - 58 s) = 0.0026 M/s

From the reaction of the general form

A + B -------------> C + D

Rate = - d[A]/dt = -d[B]/dt = d[C]/dt = d[D]/dt

$\therefore$ Here Rate of appearance of CH₃Cl will be same as disappearance of H⁺

Hence

0 to 30 s : Rate = 0.0073 M/s

30s to 58s : = 0.0042 M/s

58s to 124s: = 0.0026 M/s