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In this lesson, we will learn how to use preequilibrium and steady-state approximations to calculate overall rate constants of multi-step reactions.

Q1:

Compound D is produced with an overall rate constant π . The reaction involves three elementary reactions:

Write a balanced chemical equation for the overall reaction.

Which species act as catalysts in this reaction?

Use the preequilibrium approximation to find an expression for π in terms of the elementary reaction rate constants.

In the preequilibrium approximation, what is the rate law for the overall reaction?

Q2:

Compound A decomposes into compounds C, D and E. The decomposition involves three elementary reactions:

The rates of reaction may be estimated by using a steady-state approximation. In this approximation, the rate of change of [B] is zero.

The stoichiometry of the reaction depends on the relative rates of reactions 2 and 3. Based on the mechanism described, which of the following is not a balanced reaction equation?

Which condition must be satisfied for the steady-state approximation to be valid?

Use the steady-state approximation to find an expression for the rate of formation of C in terms of [A] and the elementary reaction rate constants.

Use the steady-state approximation to find an expression for the rate of formation of E in terms of [A] and the elementary reaction rate constants.

Q3:

A reaction proceeds via three elementary reactions:

In the steady-state approximation, the rate of change in [C] is equal to zero.

Find an expression for [C] in terms of [A], [B] and the elementary reaction rate constants.

Which condition must be satisfied for the reaction to follow Michaelis-Menten kinetics?

Q4:

Nitryl chloride ( N O C l ) 2 decomposes with an overall rate constant π . The decomposition involves five elementary reactions: Reaction 5 is the rate-determining step. The reaction may be modeled using two preequilibrium approximations:

Q5:

A reaction proceeds via four elementary reactions with an overall rate constant π :

The reaction is found to be second-order with respect to A and first-order with respect to C. Identify the rate-determining step for the reaction.

Use the pre-equilibrium approximation to find an expression for π in terms of [A], [C] and the elementary reaction rate constants.

Q6:

The decomposition of compound A proceeds via three elementary reactions:

Which condition must be satisfied for the pre-equilibrium approximation to be valid?

Under which of the following conditions would the steady-state approximation be valid but not the pre-equilibrium approximation?

In the steady-state approximation, the rate of change of [B] is zero. What is the rate of change of [B] in the pre-equilibrium approximation, in terms of [A] and the elementary reaction rate constants?

Q7:

The decomposition of compound A into compounds B and E is a first-order reaction with overall rate constant π . The decomposition involves four elementary reactions:

The rate law for this reaction is given by:

In the pre-equilibrium approximation, the rates of reactions 1 and 2 are equal. Use the pre-equilibrium approximation to find an expression for π in terms of the elementary reaction rate constants.

In the steady-state approximation, the rates of change of [C] and [D] are zero. No assumptions are made regarding [B] or the rates of reactions 1 and 2. Use the steady-state approximation to find an expression for π in terms of the elementary reaction rate constants.

Which condition must be satisfied for the pre-equilibrium and steady-state approximations to produce the same expression for π ?

Q8:

Compounds A and C react to form compound D with an overall rate constant π . The reaction involves three elementary reactions:

Which condition must be satisfied for the preequilibrium approximation to be valid?

In the preequilibrium approximation, the rates of reactions 1 and 2 are equal. Use the preequilibrium approximation to find an expression for π in terms of the elementary reaction rate constants.

In the preequilibrium approximation, what is the order of reaction with respect to A ?

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