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The reaction between solid citric acid and sodium hydrogen carbonate solution is an endothermic reaction - OCR Gateway - GCSE Chemistry: Combined Science - Question 11 - 2021 - Paper 9
Question 11
The reaction between solid citric acid and sodium hydrogen carbonate solution is an endothermic reaction. A student investigates the temperature change for the reac... show full transcript
Worked Solution & Example Answer:The reaction between solid citric acid and sodium hydrogen carbonate solution is an endothermic reaction - OCR Gateway - GCSE Chemistry: Combined Science - Question 11 - 2021 - Paper 9
Step 1
How does a temperature change show that a reaction is endothermic?
Answer
A reaction is considered endothermic if the temperature of the surroundings decreases as the reaction occurs. This happens because the system absorbs heat energy from its surroundings, leading to a drop in temperature. In this case, the temperature change experienced by the student is a decrease of 3.5 °C.
Step 2
Step 3
Describe how the student performed the experiment so that they could calculate the temperature change.
Answer
The student began by measuring and recording the initial temperature of the sodium hydrogen carbonate solution in the plastic cup. After this, they added 0.65 g of solid citric acid to the solution. The student allowed the reaction to proceed while continuously monitoring the temperature using a thermometer. Finally, they recorded the lowest temperature reached after the reaction to determine the total temperature change from the initial measurement. The temperature change was calculated by subtracting the final temperature from the initial temperature.