# When citric acid is dissolved in water and sodium hydrogencarbonate powder is added, the temperature of the mixture decreases. Explain what this temperature decrease tells us about the energy change in this reaction, and describe what is happening to energy at the particle level.

> Pearson Edexcel International GCSE Chemistry (4CH1) — 3.1 Energetics · Explain · 4 marks

> Citric acid reacts with sodium hydrogencarbonate in solution. The temperature of the surrounding solution is observed to fall during the reaction.

## Mark scheme (4 marks)

1. The reaction is endothermic
2. Energy is taken in from the surroundings (the solution / water), causing the temperature of the surroundings to decrease
3. More energy is required to break bonds in the reactants than is released when bonds in the products are formed
4. The overall energy change of the reaction is positive (the products have more energy / are at a higher energy level than the reactants)

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