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A student investigates three reactions - OCR Gateway - GCSE Chemistry: Combined Science - Question 16 - 2019 - Paper 3
Question 16
A student investigates three reactions. She wants to find out if the reactions are exothermic or endothermic. Look at her results. | Reaction | Start temperature ... show full transcript
Worked Solution & Example Answer:A student investigates three reactions - OCR Gateway - GCSE Chemistry: Combined Science - Question 16 - 2019 - Paper 3
Step 1
Which reaction, X, Y or Z, is endothermic? Explain your answer.
Answer
To determine which reaction is endothermic, we must compare the start and final temperatures of each reaction.
- For Reaction X: The start temperature is 21°C and the final temperature is 25°C. This indicates an increase in temperature, suggesting an exothermic reaction.
- For Reaction Y: The start temperature is 20°C and the final temperature is 18°C. This indicates a decrease in temperature, which is characteristic of an endothermic reaction as it absorbs heat from the surroundings.
- For Reaction Z: The start temperature is 22°C and the final temperature is 24°C. Like Reaction X, this indicates an increase in temperature, suggesting an exothermic reaction.
Thus, the endothermic reaction is Y, as it shows a decrease in temperature.
Step 2
Draw a labelled reaction profile for an endothermic reaction.
Answer
In the reaction profile for an endothermic reaction, the energy of the reactants is lower than that of the products.
- Draw a vertical line representing 'Energy' on the y-axis.
- Draw a horizontal line representing 'Progress of reaction' on the x-axis.
- Start by marking a point for 'reactants' on the left side and another for 'products' on the right side, with the products at a higher energy level.
- Label the highest point of the curve as 'activation energy', which represents the energy required to initiate the reaction.
- The curve should begin at the reactants level, rise to the activation energy, and then fall to the products level.
- Lastly, label the energy change as the difference in energy between the reactants and products.
Illustration of the profile:
Energy
|
| products
| /
| /
| / activation energy
| /
| /
| /
|_____/_____________
reactants
Progress of reaction