ExpertMedium3 marksStructured
AQA GCSE · Question 07.6 · The rate and extent of chemical change
Describe how the rate of reaction changes between 0 and 160 seconds. Use Figure 7.
Describe how the rate of reaction changes between 0 and 160 seconds. Use Figure 7.
How to approach this question
1. Understand that the rate of reaction is represented by the gradient (steepness) of the curve.
2. Look at the start of the graph (0 seconds). Describe the steepness of the curve. Is it steep or shallow? What does this mean for the rate?
3. Look at the middle part of the graph. How does the steepness change? What does this mean for the rate?
4. Look at the end of the graph. What happens to the steepness? What does this mean for the rate?
5. Combine these observations into a clear description.
Full Answer
The rate of reaction is fastest at the start (between 0 and ~60 seconds) as the curve is steepest. The rate then slows down as the curve becomes less steep. Finally, the rate becomes zero (the reaction stops) after about 120 seconds, as the curve becomes horizontal.
The rate of a reaction can be determined from the gradient (steepness) of the line on a graph of product formed vs. time.
1. **At the start (0 to ~60s):** The curve is at its steepest. This indicates that the rate of reaction is fastest at the beginning.
2. **As time progresses (~60s to ~120s):** The gradient of the curve gradually decreases, meaning the line becomes less steep. This shows that the rate of reaction is slowing down. This happens because the reactants are being used up, so their concentration decreases.
3. **At the end (after ~120s):** The curve becomes a horizontal line. A horizontal line has a gradient of zero. This indicates that the rate of reaction is zero, meaning the reaction has stopped. This occurs when one of the reactants has been completely used up.
Common mistakes
✗ Just describing the volume of gas (e.g., "the volume of gas increases") instead of the rate.
✗ Not linking the rate to the steepness of the curve.
✗ Forgetting to mention that the reaction stops.
Practice the full AQA GCSE Chemistry Foundation Tier Paper 2
60 questions · hints · full answers · grading
More questions from this exam
Q01.1This question is about copper sulfate. Blue copper sulfate turns white when it is heated. The wor...EasyQ01.2What does the symbol ⇌ mean?EasyQ01.3Complete the sentence.
The colour change when water is added to anhydrous copper sulfate is white...EasyQ01.4A student heats 2.5 g of hydrated copper sulfate in a test tube. 0.9 g of water is given off. The...EasyQ01.5Calculate the percentage of water contained in 2.5 g of hydrated copper sulfate.
(Mass of water =...Medium