Rate Law and Rate Reaction

Question

The reaction:

2 NO (g) + Cl2 (g) →2NOCl (g)

was studied at -10 Celsius. The following results were obtained where

Rate =(−) ∆[Cl2]∆t

[NO]0(mol/L) [Cl2]0(mol/L) Initial Rate(mol/L min.)

0.10 0.10 0.18

0.10 0.20 0.36

0.20 0.20 1.45

a.) What is the rate law?

b.) What is the value of the rate constant, k?

Answer 1

Find order with respect to NO and Cl₂:

With respect to NO, compare expt.# 2 and #3. Rate increases 4x when [NO] is doubled.-> 2nd order in NO.

With respect to Cl₂, compare expt.# 1 and #2. Rate increases 2x when [Cl₂] is doubles.-> 1st order in Cl₂.

a). rate = k[NO]²[Cl₂]

b). 0.18 M/min = k[0.1M]²[0.1M] = 1x10-3 M³

k = 0.18 M min^-1/1x10^-3 M³

k = 180 M^-3 min^-1