Rates Of Reaction

These help with learning about rates of reactions.

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Things to measure

Things to measure

The measurement itself depends on the nature of the reactant or product:

  • The mass of a substance - solid, liquid or gas - is measured with a balance
  • The volume of a gas is usually measured with a gas syringe, or sometimes an upside down measuring cylinder or burette

It is usual to record the mass or total volume at regular intervals and plot a graph. The readings go on the vertical axis, and the time goes on the horizontal axis.

The rate of reaction is equal to the amount of reactant used divided by the time taken. Or it can expressed as the amount of product formed divided by the time taken (http://www.bbc.co.uk/schools/gcsebitesize/science/images/add_aqa_equa_ratereac.gif)

For example, if 24 cm3 of hydrogen gas is produced in two minutes, the mean rate of reaction = 24 ÷ 2 = 12 cm3 hydrogen / min.

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Factors affecting the Rate

How to increase the rate of a reaction

The rate of a reaction increases if:

  • The temperature is increased
  • The concentration of a dissolved reactant is increased
  • The pressure of a reacting gas is increased
  • Solid reactants are broken into smaller pieces
  • A catalyst is used
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For a chemical reaction to occur, the reactant particles must collide. Collisions with too little energy do not produce a reaction.

The collision must have enough energy for the particles to react. The minimum energy needed for particles to react is called the activation energy.

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