A student collects gas every 20 s. Which calculation gives the average rate from 40 s to 80 s?
volume at 80 s−volume at 40 s40 s\frac{\text{volume at 80 s}-\text{volume at 40 s}}{40\,\mathrm{s}}40svolume at 80 s−volume at 40 s
80 sfinal volume\frac{80\,\mathrm{s}}{\text{final volume}}final volume80s
volume at 40 s+volume at 80 s2\frac{\text{volume at 40 s}+\text{volume at 80 s}}{2}2volume at 40 s+volume at 80 s
volume at 80 s×40 s\text{volume at 80 s}\times40\,\mathrm{s}volume at 80 s×40s
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.