CHEM 104 Homework 4 2. 20 points-Ch. 16.4, 16.6 Nitric oxide (NO) is a reactive
ID: 1084436 • Letter: C
Question
CHEM 104 Homework 4 2. 20 points-Ch. 16.4, 16.6 Nitric oxide (NO) is a reactive gas that contributes to acid rain and ozone depletion in the atmosphere. It can be reduced with hydrogen gas to form harmless nitrogen gas and water, according to the following reaction: a) This reaction is known to be first order in H2 and second order in NO. Write the overall rate law for the reaction. When the reaction is run with a large excess of H2gas, the [H2] term can be ignored in the rate law, simplifying it to Rate k'[NO. Ifk 6.0x10 L/mol-s when [Ha] - 1.00 M, how long will a reaction of [NO]: 0.00025 M take to reach 95% completion? Two possible mechanisms for the reaction are given below. Which one is more consistent with the observed rate law? Explain your choice b) c) Mechanism 1 Slow FastExplanation / Answer
the given reaction is,
2 No (g) + 2 H2 (g) ------> N2 (g) + 2 H2O (g)
Rate law = k [NO]^2 [H2]^1
when [H2] is taken in excess then rate law is given by ,
rate law = k [NO]^2
for second order reaction the rate constant is given by,
K = 1/t((1/a-x) - (1/a))
where (a-x) = remaining concentration
a = initial concentration
t = time taken for that completion
After 95% completion [NO] = 0.00025 = (100 - 95) = 5% of initial [NO]
initial concentration of [NO] = 0.00025*100/5 = 0.005
so
K = 1/t((1/a-x) - (1/a))
6 * 10^4 = 1/t((1/0.00025) - (1/0.005))
t = 0.0633 sec
Mechanism 2 is favourable since in the rate law,
Rate = k [NO]^2 [H2]^1
Order of reaction is 2 with respect to [NO] and order of reaction is 1 with respect to [H2].
So the order is decided based on the specices involved in the slow step of mechanism hence the Mechanism 2 is prefered.