Question

Consider the gas-phase reaction between nitric oxide and bromine at 273 ?C
2NO(g)+Br2(g)?2NOBr(g).
The following data for the initial rate of appearance of NOBr were obtained:

Experiment	[NO](M)	[Br2](M)	Initial Rate of Appearance of NOBr(M/s)
1	0.10	0.20	24
2	0.25	0.20	150
3	0.10	0.50	60
4	0.35	0.50	735

rate=k[NO]2[Br2]

Calculate the average value of the rate constant for the appearance of NOBr from the four data sets.

k= _______ M^-2s^-1

What is the rate of disappearance of Br2 when [NO]= 8.1

Answer 1

For the first part what you are going to do is plug in the numbers and solve for k.

Experiment 1: 24M/s=k[0.10M]²[0.20M]

24M/s=k(0.002)M³

k=12000M^-2s^-1

k is a constant at any given temperature so the value will be the same regardless of the concentration. I will find k for experiment 2 to exemplify this.

Experiment 2: 150M/s=k[0.25M]²[0.20M]

150=k(0.0125)M³

k=12000M^-2s^-1

Part 2: You are going to plug in the value you figured out previously for k and then plug in the two concentrations and solve for rate.

Rate=k[NO]²[Br]

Rate=12000M^-2s^-1[8.1*10^-2M]²[0.34M]

Rate=26.8M/s

This number (26.8) is the rate of 1 mol of the reaction. So then to solve for the disappearance of Br₂ you will:

26.8M/s*(1mol of Br₂/1 mol reaction), which will yield the 26.8M/s disappearance rate.