A colourless reaction mixture gradually turns green as a product forms. An electronic sensor records the colour intensity in arbitrary units. A larger reading means that more product has formed.
The table shows the results.
| Time in s | 0 | 30 | 60 | 90 |
|---|---|---|---|---|
| Colour intensity in arbitrary units | 0 | 36 | 60 | 60 |
Calculate the mean rate of change of the colour intensity during the first 30 s.
A student claims that the reaction continued at a steady rate between 60 s and 90 s.
Explain whether the readings support this claim.
The sensor is unavailable for a second investigation, so the student judges by eye when a fixed green colour is reached.
Explain why the same observer should judge the colour in every experiment.
122 exam-style questions on Edexcel GCSE Chemistry 8.1 Rates of reaction, covering 8.1.1 Measuring and interpreting rates of reaction, 8.1.2 Collision theory and the factors affecting rate, and 8.1.3 Catalysts and enzymes. Each one has a worked solution and a mark scheme showing where the marks go.