Question

When the reaction

CH3Cl(g) + H2O(g) →CH3OH(g) + HCl(g)

Was studied, the tabulated data were obtained. Based on thesedata, what are the reaction orders?

Initial Concentrations, M; Initial Rates,Ms-1

Exp CH3Cl H2O Rate, Ms-1

1 0.100 0.100 0.182

2 0.200 0.200 1.45

3 0.200 0.400 5.81

A. CH3Cl: firstorder H2O:first order

B. CH3Cl: second order H2O: first order

C. CH3Cl: firstorder H2O: second order

D. CH3Cl: second order H2O: second order
Please EXPLAIN your answer.

Answer 1

The reaction orders for CH3Cl and H2O are determined to be second order for both reactants as evidenced by the quadrupled rate increase when their concentrations are doubled. So the correcct option is D.

Step-by-step explanation:

To determine the reaction orders for CH3Cl and H2O in the given reaction, we analyze the provided experimental data by comparing initial concentrations and initial rates.

1. Comparing Experiment 1 and Experiment 2: The concentration of both CH3Cl and H2O is doubled, and the rate increases from 0.182 to 1.45, an 8-fold increase. This suggests that both are of second order because doubling the concentration of a second-order reactant increases the rate by a factor of 22, which is 4, and since both reactants are doubled, 4*4=16, accounting for the 8-fold increase.
2. Comparing Experiment 2 and Experiment 3: Only the concentration of H2O is doubled, and the rate increases from 1.45 to 5.81, a 4-fold increase. This change indicates that H2O is second-order because doubling the concentration of a second-order reactant increases the rate by a factor of 22 or 4.

Based on these observations, the answer is D. CH3Cl: second order and H2O: second order. Both the concentrations of CH3Cl and H2O have a squared relationship to the rate, characteristic of second-order reactions.

Answer 2

We can express the rate equation in this form:
-r = k A^n B^m

where -r is the rate
k is the rate constant,
A is the concentration of CH3Cl
n is the order with respect to CH3Cl
B is the concentration of H2O
m is the order with respect to H2O

We can solve this by trial and error or by calculus. The first method is easier. The rate constant does not depend on the concentration of the reactant. Assume values of n and m and solve for k in each experiment. The only option that gives really close values of k in each experiment is:
C. CH3Cl: firstorder H2O: second order