Factors that Affect the Rate of Reaction

  • There are several factors that can affect the rate of a reaction. These are:
    • Concentration of the reactants in solution or the pressure of reacting gases
    • Surface area of solid reactants
    • Temperature at which the reaction is carried out
    • The use of a catalyst
  • Changes in these factors directly influence the rate of a reaction.
  • It is of economical interest to have a higher rate of reaction as this implies a higher rate of production and hence more profit.
  • The following graphs explain

Concentration of a solution/pressure of reacting gases

Concentration of solution, IGCSE & GCSE Chemistry revision notes

Graph showing the effect of the concentration of a solution and gas pressure on the rate of reaction

Explanation:

  • Compared to a reaction with a reactant at a low concentration, the graph line for the same reaction but at a higher concentration/pressure has a steeper gradient at the start and becomes horizontal sooner.
  • This shows that with increased concentration of a solution, the rate of reaction will increase.

Surface area of a solid

Surface Area of a Solid Reactant, IGCSE & GCSE Chemistry revision notes

Diagram showing the effect of the surface area of a solid on the rate of reaction

Explanation:

  • Compared to a reaction with lumps of reactant, the graph line for the same reaction but with powdered reactant has a steeper gradient at the start and becomes horizontal sooner.
  • This shows that with increased surface area of the solid, the rate of reaction will increase.

Temperature

Temperature Diagram, IGCSE & GCSE Chemistry revision notes

Graph showing the effect of temperature on the rate of reaction

Explanation:

  • Compared to a reaction at a low temperature, the graph line for the same reaction but at a higher temperature has a steeper gradient at the start and becomes horizontal sooner.
  • This shows that with increased temperature, the rate of reaction will increase.

Catalyst

Effect of using catalyst, IGCSE & GCSE Chemistry revision notes

Graph showing the effect of the use of a catalyst on the rate of reaction

Explanation:

  • The diagram shows that when a catalyst is used, the activation energy is reduced as it creates an alternative pathway requiring lower activation energy, allowing more successful and frequent collisions.
  • This shows that when a catalyst is used, the rate of reaction will increase.

Required Practical 5: Investigating Effect of Concentration on Rate of Reaction

Required Practical 5(a): Effect of Concentration of Reactant – PrecipitationR Reaction

Objective:
To investigate the effect of changing concentration on the rate of reaction by measuring the formation of a precipitate.

Hypothesis:
A precipitate will be formed quicker if the concentration of the reactants is greater.

Materials:

  • 40 g/dm3 sodium thiosulfate solution
  • 1.0 mol/dm3 dilute hydrochloric acid
  • conical flask (100 cm3)
  • printed black cross on paper
  • room with unchanging light conditions
  • white paper or white tile
  • stopclock

Investigating effect of concentration on rate reaction, IGCSE & GCSE Chemistry revision notes

Diagram showing the apparatus needed to investigate reaction rate in a precipitation reaction

Practical Tip:
The same person should be the one recording the time taken for the cross to disappear as this measurement is open to bias as it is based on human perception.

Method:

  1. Measure 50 cmm3 of Nam2S2O3 solution into a flask.
  2. Measure 5 cmm3 of dilute HCl into a measuring cylinder.
  3. Draw a dark cross on a piece of clean white paper and put it underneath the flask.
  4. Add the acid into the flask and immediately start the stopwatch.
  5. Solid sulfur is formed which precipitates in solution, turning cloudy:
    • Na2S2O3 + 2HCl → 2NaCl + S + SO2 + H2O
  6. Look down at the cross and stop the timing when the cross can no longer be seen.
  7. Repeat using different concentrations of sodium thiosulfate solution (mix different volumes of sodium thiosulfate solution with water to dilute it).

Results: Record your results in a suitable table, eg:

Required Practical 5(a) Table, IGCSE & GCSE Chemistry revision notes
Evaluation:
Plot a graph of the results with time on the x-axis and the concentration of Na2S2O3 on the y-axis. With an increase in the concentration of a solution, the rate of reaction will increase so the time for the cross to disappear decreases.
Conclusion:
As there are more reactant particles in a given volume collisions occur more frequently, increasing the rate of reaction.

Required Practical 5(b): Effect of Concentration of a Reactant – Gas Volume

Objective:
To investigate the effect of changing concentration on the rate of reaction by measuring the volume of gas given off.

Hypothesis:
The same amount of gas will be produced in less time if the concentration of reactants is increased.

Materials:

  • magnesium ribbon cut into 3 cm lengths
  • sulfuric acid 1 mol dm-3 and 1.5 mol dm-3
  • conical flask (100 cm3)
  • safety goggles
  • gas syringe
  • stop clock

Rate of Reaction - Gas Syringe, IGCSE & GCSE Chemistry revision notes

Diagram showing the apparatus needed to investigate reaction rate by measuring gas volume

Practical Tip:
Magnesium and sulfuric acid will react immediately so the flask must be connected to the gas syringe straight after adding the magnesium to avoid gas escaping.

Method:

Measure 50 cm3 of 1.0 mol dm-3 H2SO4 solution into a flask.
Add the magnesium ribbon to the flask and connect it to the gas collection equipment.
Start the stopwatch and record the volume of gas every 10 seconds.
When the reaction is complete, repeat using 1.5 mol dm-3 sulfuric acid.

Results: Record your results in a suitable table, eg:

Required Practical 5(b) Table, IGCSE & GCSE Chemistry revision notes

Evaluation:
Plot a graph of the results with time on the x-axis and the concentration and the volume of gas on the y-axis. With an increase in the concentration of a solution, the rate of reaction will increase so the volume of gas increases.

Conclusion:
As there are more reactant particles in a given volume collisions occur more frequently, increasing the rate of reaction.

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Morgan Curtin Chemistry

Author: Morgan

Morgan’s passion for the Periodic Table begun on his 10th birthday when he received his first Chemistry set. After studying the subject at university he went on to become a fully fledged Chemistry teacher, and now works in an international school in Madrid! In his spare time he helps create our fantastic resources to help you ace your exams.