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Rate Mechanisms and Their Structure

Please show all work and keep things as simple as possible in the following three problems on chemistry and its rate mechanisms.

The Rate Law.
1) A possible mechanism for the reaction between H2 and CO is shown below, where RDS is the rate-determining step. What is the rate law for the overall reaction?

H2 ? 2 H
HCO (RDS) ? H + CO
H2CO ? H + HCO

2) A possible mechanism for the reaction of NO with O2 is shown below, where RDS is the rate-determining step. What is the rate law for the overall reaction?

N2O2 ? NO + NO
NO2 + NO + O (RDS) ? N2O2 + O2
NO2 ? NO + O

Reaction Mechanisms for Reaction 2
3) There are four possible mechanisms for the reaction 2 NO2 + Cl2 shown below, where RDS is the rate-determining step. The experimentally determined rate law is first-order in NO2Cl. Explain which mechanisms are reasonable and which are not reasonable.

Mechanism 1
NO2Cl + NO2Cl ? 2 NO2 + Cl2 ?

Mechanism 2
NO2 + Cl (RDS) ?NO2Cl
NO2Cl + Cl NO2 + Cl2 ?

Mechanism 3
NO + OCl ? NO2Cl
NO3 + Cl2 ? NO2Cl + OCl (RDS)
2 NO2 ? NO + NO3

Mechanism 4
N + O2Cl (RDS) ? NO2Cl
NO4 + Cl2 ? O2Cl + NO2Cl
N2O4 ? NO4 + N

Catalysis. Acetaldehyde can undergo catalytic decomposition according to the mechanism below:
CH3I + HI + CO (RDS) ? CH3CHO + I2
CH4 + I2 ? CH3I + HI

Use the mechanism to determine: i) the overall chemical equation, ii) the catalyst, iii) the intermediates, and iv) the rate law.

Solution Preview

1) Recall the following:
H2 ? 2 H
HCO (RDS) ? H + CO
H2CO ? H + HCO

Since the second step is the rate determining step, this step is used to determine the rate law. The general rate law equation is Rate = (k[A]^(x))([B]^(y)) where k is the rate coefficient, A and B are reactants, and x and y are orders for those reactants. Thus, the rate law for this overall reaction is Rate = k [HCO]^(x)

2) Recall the following:
N2O2 ? NO + NO
NO2 + NO + O (RDS) ? N2O2 + O2
NO2 ? NO + O

Since the second step is the rate determining step, it is used to find the rate law. Thus, the rate law for this mechanism is Rate = k([NO2]^x))([NO]^(y))([O]^(z))

3) Recall the following:
Mechanism 1
NO2Cl + NO2Cl ...

Solution Summary

This solution addresses the rate laws of mechanisms of different chemical reactions, as well as the appropriateness of the mechanisms themselves to determine chemical reactions. The answers below look at two specific cases where rate laws are determined in accordance with the overall chemical reaction, as well as an assortment of possible mechanisms to choose from for a specific chemical reaction.

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