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Kinetics

Catalysts and the activation energy barrier

  • 3 things to know
  • Unit AS 2

Overview

What a catalyst does to a chemical reaction, how a catalyst changes the reaction profile of a reaction and catalyst used in the Haber process.

What you need to know

Answer each one before you reveal it.

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Key term

State what a catalyst does to a chemical reaction.

Key term

How is the effect of a catalyst shown on a Maxwell–Boltzmann diagram?

Key term

Why does moving the activation energy line to the left increase the rate so markedly?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    State what a catalyst does to a chemical reaction.

    Model answer

    A catalyst increases the rate of the reaction and is recovered chemically unchanged at the end of it.

  2. 2

    By what means does a catalyst increase the rate of a reaction?

    Model answer

    It provides an alternative reaction pathway that has a lower activation energy than the uncatalysed route.

  3. 3

    How is the effect of a catalyst shown on a Maxwell–Boltzmann diagram?

    Model answer

    A second vertical line is drawn further to the left, at the lower activation energy of the catalysed route.

  4. 4

    Does adding a catalyst change the shape of the Maxwell–Boltzmann curve?

    Model answer

    No, the shape of the curve depends only on the temperature, which the catalyst does not alter.

  5. 5

    Why does moving the activation energy line to the left increase the rate so markedly?

    Model answer

    A far greater area of the curve then lies to the right of the line, so many more molecules have enough energy to react on collision.

  6. 6

    Describe how a catalyst changes the reaction profile of a reaction.

    Model answer

    The hump between the reactant and product levels is lowered, while the positions of the two levels themselves are unchanged.

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