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AQA GCSE · Question 02.4 · Energy changes
Figure 2 represents the reaction profile of the catalysed reaction between ammonia and oxygen.
Complete the reaction profile for the catalysed reaction in Figure 2.
You should:
• label the activation energy
• label the reactants and products, using the names of the reactants and products.
Figure 2 represents the reaction profile of the catalysed reaction between ammonia and oxygen.
Complete the reaction profile for the catalysed reaction in Figure 2.
You should:
• label the activation energy
• label the reactants and products, using the names of the reactants and products.
How to approach this question
1. Identify the reactants and products from the word equation given in the previous question part (ammonia + oxygen → water + nitric acid). Reactants are always on the left of the profile, and products are on the right.
2. Recall the definition of activation energy. It is the minimum energy required to start a reaction. On a reaction profile, it is represented by the "hump" from the reactants' energy level to the peak of the curve.
3. Draw a double-headed arrow to represent this energy difference and label it correctly.
Full Answer
The completed reaction profile should show:
1. "Ammonia + oxygen" written on the initial flat line on the left.
2. "Water + nitric acid" written on the final flat line on the right.
3. A double-headed arrow drawn from the reactants' energy level to the peak of the curve, labelled "Activation energy".
A reaction profile diagram shows the change in energy during a chemical reaction.
- **Reactants and Products:** The horizontal line at the start represents the energy of the reactants (ammonia and oxygen). The horizontal line at the end represents the energy of the products (water and nitric acid). Since the products are at a lower energy level than the reactants, this is an exothermic reaction.
- **Activation Energy (Ea):** The peak of the curve represents the transition state. The activation energy is the energy difference between the reactants and the transition state. It is the minimum amount of energy that must be supplied to the reactants for the reaction to occur. It is shown as an arrow pointing upwards from the reactant energy level to the peak of the curve.
Common mistakes
✗ Swapping the labels for reactants and products.
✗ Labelling the overall energy change (enthalpy change) instead of the activation energy.
✗ Drawing the activation energy arrow from the x-axis, not from the reactant energy level.
Practice the full AQA GCSE Chemistry Higher Tier Paper 2
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