Rate of reaction and collision theory

  • Created by: jaaaz_v
  • Created on: 04-05-15 15:21

The rate of a reaction

This depends on:

  • Temperature
  • Concentration
  • Catalyst
  • Surface area

You can calculate the rate of a reaction using the formula:

Amount of reactant used / time


Amount of product formed / time

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Measuring the rate of a reaction (Precipitation)


  • This is when the product of a reaction turns the solution cloudy.
  • You can measure how long this takes by placing something underneath the solution (e.g. a piece of paper with an "x" on it), and recording how long it takes for it to dissapear. 
  • The quicker it dissapears, the faster the reaction.
  • The results of this observation aren't very accurate
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Measuring the rate of a reaction (Change in mass)

Change in mass

  • You can measure the speed of a reaction that releases gas on a mass balance.
  • As gas is given off the mass decreases.
  • The quicker the reading on the mass balance decreases, the quicker the rate of reaction.
  • You can easily plot graphs of the results of this method.
  • This is the most accurate way of measuring the rate of reaction because the measurements taken by the mass balance are accurate.
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Measuring the rate of a reaction (Volume of gas gi

Volume of gas given off

  • You can measure this by attaching a gas syringe to an experiment. 
  • The more gas thats released in a given time, the faster the rate of the reaction.
  • You could plot a graph comparing time with the amount of gas released with the results of this method.
  • Most gas syringes give the volume to the nearest mililitre, so they're rather accurate.
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Collision theory

Chemical reactions can only occur when reacting particles collide with enough energy. The amount of energy that's needed for particles to react is called activation energy.

Temperature, concentration, surface area, and the presence of catalysts all effect the amount of successful collisions that take place in a reaction.

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Collision theory (Temperature)

Increasing the temperature of a reaction increases the speed of the particles. This means that the particles can collide more frequently and energetically. This increases the rate of reaction.

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Collision theory (Concentration)

When the concentration is increased, there are more particles, which increases the likelihood of reactions. The particles are more squashed together, so collisions are more frequent.

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Collision theory (Surface area)

Increasing the surface area of solid reactants increases the frequency of collisions and increases the rate of reaction. This is because the particles have more area to work on, so collisions will be more frequent.

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Collision theory (Catalysts)

A catalyst is s aubstance which speeds up a reaction without being changed or used up in the reaction.

Catalysts give the particles a larger surface to stick to, which increases the number of successful collisions. 

They're important for increasing the rates of reactions in industrial processes, and help to reduce costs.

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