Teacher's notes and answers to questions in the book - Hodder Plus ...

WJEC GCSE Additional Science Teacher’s Notes
9. Calculate the rate of reaction at the steepest part of your graph by drawing a tangent line and
measuring the gradient (the units will be g/s).
Student measurements from their own graph.
Measuring reactions involving changes of ligh transmission through a
precipitate
10. What is the pattern/shape of your graph
The graph will be a negative curve with decreasing negative gradient.
11. What does your graph tell you Where is the rate of reaction fastest
The rate of reaction is highest at the start of the reaction and it gradually decreases with
time.
12. Can you tell when the reaction is complete
The reaction is complete when the light transmission of the system stays constant for a
period of time.
Questions
1. What is meant by the rate of a reaction
How much reaction product is produced in a set time.
2. Explain how you use a graph to measure the rate of a reaction.
Draw a tangent line to the reaction curve at any point in time – the rate of reaction is the
gradient (slope) of the line.
3. How can you tell from a rate of reaction graph where the reaction is:
a fastest
The rate of reaction is fastest where the gradient is biggest (where the slope is steepest).
b complete
The reaction is complete where the graph is horizontal, when the gradient is zero.
4. In a calcium carbonate and hydrochloric acid experiment, a student collects the carbon dioxide gas and
produces the rate of reaction graph shown in Figure 11.10. On a copy of this graph, sketch the graph
you would expect from similar experiments carried out with:
a acid of twice the concentration, but at the same temperature
The rate of reaction will be the same, as this is limited by the concentration of the acid not
the amount.
b the same amount of each chemical, but carried out at a higher temperature.
A higher temperature means a faster rate of reaction, but as the amount of chemicals is
fixed, the final volume of gas will be the same.
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