AP Chemistry Rate Question

Question

The reaction:

 

2NO(g) +Cl2(g)====> 2NOCl (g)

 

was studied at -10°C. The following results were obtained were: Rate= -(change in Cl2 concentration)/(change in time)

 

[NO]0 (mol/l)     [Cl2]0(mol/l)  Initial rate

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

Answer 1

Doubling [NO] while holding [Cl₂] constant leads to a 4 fold increase in rate.  Compare 0.36 v. 1.45. Thus the reaction is 2nd order with respect to [NO]

Doubling [Cl₂] while holding [NO] constant leads to a doubling of rate. Compare 0.18 v. 0.36.  Thus the reaction is 1st order with respect to [Cl₂].

Rate law is:  rate = k[NO]²[Cl₂]

To solve for k, use one of the rates and the corresponding concentrations and plug them into the rate law.

0.18 = k(0.1)²(0.1)

k = 0.18/0.001 = 180 units are 1/[ ]

Do the same with the other values and take an average to obtain an average value of k