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Rates of reaction

Factors affecting the rates of reaction

You will be expected to remember the factors that affect the rate of reactions, and to plot or interpret graphs from rate experiments.

How to increase the rate of a reaction

The rate of a reaction increases if:

  • The temperature is increased
  • The concentrationconcentration: The concentration of a solution tells us how much of a substance is dissolved in water. Concentration is measured in moles per dm3. The higher the concentration, the more particles of the substance are present. of a dissolved reactant [reactant: Substances present at the start of a chemical reaction ] is increased
  • The pressure of a reacting gas is increased
  • Solid reactants are broken into smaller pieces
  • A catalystcatalyst: A catalyst changes the rate of a chemical reaction without being changed by the reaction itself. is used
Graph showing rates of reaction under changing conditions. At a lower temperature, lower concentration, or with larger pieces, the rate of reaction is slower than at higher temperatures, higher concentrations, or with smaller pieces

Rate of reaction and changing conditions

The graph above summarises the differences in the rate of reaction at different temperatures, concentrations and size of pieces. The steeper the line, the greater the rate of reaction. Reactions are usually fastest at the beginning, when the concentration of reactants is greatest. When the line becomes horizontal, the reaction has stopped.

Back to Chemical reactions index

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