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Factors affecting Reaction Rate

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More Lessons for IGCSE Chemistry
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A series of free IGCSE Chemistry Activities and Experiments (Cambridge IGCSE Chemistry).

The rate of reaction tells us how rapidly the products are made from the reactants.
How to measure the rate of reaction?
1. Measure the volume gas produced at regular time intervals.
2. Measure the decrease in mass of the reactants at regular time intervals.
3. Measure the time taken for a colour change to occur, or for the solution to become opaque.

Collision Theory
The Activation Energy for each reaction is the amount of energy needed to break the bonds in the reactants.
and how it enables us to predict how different conditions will affect the rate of a reaction.
Factors which affect the rate of reaction:
• temperature of the reactants
• pressure (only applies to gases)
• concentration of reactants (applies to solutions)
• surface area (applies to solid reactants)
• use of a catalyst

Examples of experimental methods to determine the rate of a reaction, and the role of catalysts.

How does concentration affect the rate of reaction?
In this activity, we want to investigate how concentration affects the rate of the following chemical reaction:
2Mg(s) + 2HCl(aq) → 2MgCl(aq) + H2(g)

1. Cut the magnesium ribbon into 5 equal pieces, each with the length of 2.5 cm
2. Label 5 test tubes A, B, C, D and E.
3. Pour 20 ml of HCl into test tube A, 18 ml into test tube B, 16 ml into test tube C, 14 ml into test tube D and 12 ml into test tube E.
4. Add water into test tube B, C, D and E until the solution reaches 20 ml.
5. Put a magnesium strip into test tube A and record the time it takes for the strip to completely react. Repeat for test tubes B, C, D and E. 6. Plot a graph from your results and state you conclusion.
(The following video shows an experiment conducted by students. They are quite a number of errors in the video. Try to spot them.) Questions
1. In the above, experiment what are the variables that need to be held constant?
2. What were some of the errors that you detected in the video?
3. What could be another way that we can measure the rate of reaction for the above experiment?

  • Show Solutions
    1. Size of the magnesium strip. Volume of solution.
    2. The given equation for magnesium and hydrochloric acid was not balanced. Care was not taken to measure the volume of the acid accurately. Some of the acid was spilled when poured into the test tube. The experiment should be repeated to improve the reliability of the results, by calculating an average of our results. and to spot anomaly.
    3. We can measure the time that it takes for a certain amount of gas (hydrogen) to be produced.
Rates of Reaction
Catalytic Converters
Factors that Affect the Rate of Reaction
Measuring Rates of Reaction
Collision Theory
Interpreting Rates of Reaction Graphs

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