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Chemical Kinetics

The rate equation, order and the rate constant

  • 3 things to know
  • Component 1

Overview

Order of reaction with respect to a particular reactant, overall order of a reaction and rate constant of a reaction.

What you need to know

Answer each one before you reveal it.

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Key term

Write the general form of the rate equation for a reaction involving reactants A and B.

Key term

State the units of the rate constant for a second-order reaction.

Key term

State the units of the rate constant for a reaction that is third order overall.

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    Write the general form of the rate equation for a reaction involving reactants A and B.

    Model answer

    rate = k[A]ᵐ[B]ⁿ, where m and n are the orders with respect to A and B.

  2. 2

    Define the order of reaction with respect to a particular reactant.

    Model answer

    It is the power to which the concentration of that reactant is raised in the rate equation.

  3. 3

    Define the overall order of a reaction.

    Model answer

    It is the sum of the powers of all the concentration terms appearing in the rate equation.

  4. 4

    What is the rate constant of a reaction?

    Model answer

    It is the constant of proportionality k in the rate equation, which has a fixed value for a given reaction at a given temperature.

  5. 5

    Can the orders of a reaction be deduced from its balanced equation?

    Model answer

    No, orders can only be found by experiment, because they depend on the mechanism rather than on the overall stoichiometry.

  6. 6

    State the units of the rate constant for a zero-order reaction.

    Model answer

    They are mol dm⁻³ s⁻¹, the same as the units of the rate itself.

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AThe equation is k = A exp(−Ea/RT).
BHere k is the rate constant.
CA is the pre-exponential factor.

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Kc is a fixed number at a given temperature.
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