GCSE Combined Science (AQA)

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Rate of Reaction

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The rate and extent of chemical change Rate of reaction

Rate of Reaction

10:50 Calculating Reaction Rates
Spec 4.6.1.1
Previous Concentration of Solutions (g/dm3) Next Temperature & Rate
  • The rate of reaction measures how quickly a reaction occurs.
  • Different chemical reactions have varying rates.
  • Fireworks demonstrate fast reactions with loud sounds and bright lights.
  • Rusting of metals is a slow reaction, taking months or years.
  • The rate of a chemical reaction changes as it progresses.
  • Example: Metal with acid reaction starts vigorously, indicated by hydrogen bubbles.
  • Reaction slows down as metal decreases and acid becomes less concentrated.
  • Mean rate of reaction is often calculated.
  • Mean rate of reaction can be calculated using:
  • Quantity of reactant used divided by time taken.
  • Quantity of product formed divided by time taken.
  • Measuring reactant loss or product formation helps determine reaction rate.
  • Mass is measured in grams, typically for reactant used.
  • Volume is measured in centimeters cubed, typically for product gas.
  • Time is measured in seconds for rate calculations.
  • Units for rate of reaction are grams per second or centimeters cubed per second.
  • Example calculation: Mean rate of reaction between magnesium and hydrochloric acid.
  • Steps for calculation:
  • 1. Write out the equation to be used.
  • 2. Identify when the reaction finished and maximum product formed.
  • 3. Write down total quantity of product formed and time taken.
  • 4. Substitute values into the equation and calculate.
  • 5. Check units for the rate of reaction.
  • Units for rate should always be given, even if not explicitly asked.

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