CHM 123HW 3 – Chemical KineticsName

Due Monday 4/27/15

  1. (5pts) Cows digesting grass emit large quantities of global-warming methane gas into the atmosphere. As an atmospheric chemist, you are interested in knowing what role that methane plays in the cycling of chlorine in the atmosphere via the reaction:

Cl(g) + CH4(g) → CH3Cl(g) + H(g)

The rate constant at 25.0 °C is 6.02×107 M-1s-1. At 65,000 ft in the stratosphere, where the temperature is -60.0 °C, the rate constant is 1.08×107 M-1s-1.What is the activation energy for this reaction?

2.The reaction 2 NOCl 2 NO + Cl2 has k = 9.3 x 10–5 L mol–1 s–1 at 100 ºC and an activation energy of 99 kJ/mol.

a. (5pts) What is the rate constant at 130 ºC?

b. (5pts) At what Celcius temperature will the rate constant be 5.1 x 10–7 L mol–1 s–1?

  1. (5pts) In automobile exhausts, the following reaction can occur between nitrogen dioxide and carbon monoxide.

NO2(g) + CO(g) → NO(g) + CO2(g)

To design better emission control systems, chemists need to know as much as possible about the kinetics of this reaction. The experimental rate law is rate = k[NO2]2. Explain and show which of the two mechanisms below better represents this reaction.

Mechanism A Mechanism B

NO2  NO + O 2NO2  NO3+ NO

CO + O  CO2CO + NO3  NO2 + CO2

  1. Consider the following mechanism for a reaction

BrCl + H2⇌HBr + HCl fast

HCl + BrClHBr + Cl2slow

  1. (2pts) Write the chemical equation for the overall reaction
  1. (2pts) What is/are the intermediate(s) in the mechanism?
  1. (3pts) Write the rate law for the overall reaction. (This is trickier than it looks. Be careful)
  1. Consider the exothermic reaction between reactants A and B?

Step 1A + B → E (fast)

Step 2E + B → C + D (slow)

  1. (2pts) What is the molecularity of step 1 and step 2
  1. Write an overall equation
  1. (3pts) What is the rate law for the reaction?
  1. (5pts) Sketch a potential energy diagram for this reaction. Identify the activation energy for the overall forward reaction. Identify the location of reactants, intermediate(s), activated complex(es), and products.

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