The initial rate data at 25 o C are listed for the reaction NH 4 + (aq) + NO 2 -
ID: 818876 • Letter: T
Question
The initial rate data at 25 oC are listed for the reaction
NH4+ (aq) + NO2-1 -> N2(g) + H2O(l)
Experiment
Initial [NH4+1]
Initial [NO2-1]
Initial rate (M/s)
1
0.24
0.10
7.2 X10-6
2
0.12
0.10
3.6 X 10-6
3
0.12
0.15
5.4 X 10-6
a. Determine the rate law
b. Determine the value of the rate constant.
c. What is the reaction rate when the concentrations are [NH4+1] = 0.39 M and [NO2-1] = 0.052 M.
Experiment
Initial [NH4+1]
Initial [NO2-1]
Initial rate (M/s)
1
0.24
0.10
7.2 X10-6
2
0.12
0.10
3.6 X 10-6
3
0.12
0.15
5.4 X 10-6
Explanation / Answer
a. Compare the ratio of the rates to the ratios of the concentrations to find the powers of the reactants in the rate law. Make sure you choose two concentrations that vary while the concentrations of the other reactant are the same.
(7.2x10^-6) / (3.6x10^-6) | 0.24/0.12
2 and 2 --> 2^1 = 2, therefore the exponent of NH4+ is 1
(5.4x10^-6) / (3.6x10^-6) | 0.15/0.10
1.5 and 1.5 --> 1.5^1 = 1.5, therefore the power of NO2-1 is 1
rate law is rate = k[NH4+][NO2-]
b.
Use a rate from the table and plug it into the rate law to find k
7.2 x 10^-6 M/s = K(0.24 M)(0.10 M)
k = 3.0 x 10^-4 M^-1s^-1
c.
rate = (3.0x10^-4)(0.39)(0.052)
rate = 6.1 x 10^-6 M/s
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