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National 5 level writing and balancing equations. If you need to practise this access the National 5 Chemistry Skills resource |
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In this question, the term average can be confusing. We call it an average rate because the rate is changing as the reaction proceeds in the first 15 minutes of the reaction, as shown by the changes in the values. ( A constant rate would produce a constant change).
The average rate is simply calculated in these circumstance by examining the change in quantity and dividing that by the time taken.
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For this question, it is important that you consider the starting conditions of any chemical reaction. All reactants are at their highest concentrations. As the reaction proceeds, the concentration of the reaction will decrease. This will allow you to establish if the rate rises or falls. |
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You know from the graph the starting mass, you know the final mass – so you can calculate how much has been used by the end of the reaction [that the line falls to a straight horizontal line indicates the reaction has reached an end point].
Read from the graph when half this mass has been lost. This time would be the half life. |
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All mass lost from the reaction is due to the production of carbon dioxide gas. Your graph must reflect your understanding of the change in rate with time.
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