6.1.3

Catalysts

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Rate of Reaction - Key Factors

The main factors that affect the rate of chemical reactions are:

Illustrative background for Concentration of dissolved reactantsIllustrative background for Concentration of dissolved reactants ?? "content

Concentration of dissolved reactants

  • Increasing the concentration increases the collision frequency. This increases the rate of reaction.
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Pressure of gas reactants

  • Increasing pressure is like increasing the concentration.
  • It has the same outcome of increasing the collision frequency, which increases the rate of reaction.
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Temperature

  • Increasing the temperature increases the rate at which collisions happen.
  • Increasing the temperature increases the energy of reactant particles. This means that a greater proportion of the particles will have more energy than the activation energy that is needed.
  • Together, these lead to more successful collisions. This increases the rate of reaction.
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Surface area of solid reactants

  • Increasing the surface area increases the collision frequency. This increases the rate of reaction.
  • This is often done by breaking up solids into smaller lumps (e.g. powders).
  • This increase in surface area to volume ratio makes sure that more particles are exposed to attack.
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Catalysts

  • Substances that increase a chemical reaction's rate without reducing in quantity during the reaction are called catalysts.

Catalysts

Catalysts increase the rate of chemical reactions by lowering the activation energy. They do this by changing the reaction pathway.

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Are catalysts used up in reactions?

  • Catalysts are not used up during chemical reactions. This means that:
    • They can be reused indefinitely.
    • They are not found in chemical equations.
  • But, catalysts will often need cleaning or regenerating, which has knock-on effects for energy expenditure and environmental impact.
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What are some examples of catalysts?

  • Different catalysts are appropriate for different reactions:
    • Iron is used in the process that makes ammonia.
    • Platinum and palladium are used in catalytic converters in cars.
    • Enzymes catalyse reactions in biological systems.
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What form do catalysts come in?

  • Catalysts often come as powders, pellets or fine gauzes because these types of substance have particularly high surface areas.

Jump to other topics

1Atomic Structure

2Chemical Bonding

3Quantitative Chemistry

4Chemical Changes

5Energy Changes

6The Rate & Extent of Chemical Change

7Organic Chemistry

8Chemical Analysis

9Chemistry of the Atmosphere

10Using Resources

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