What is an exothermic reaction?
Name the instrument used to accurately measure the calorific values of different foods - Leaving Cert Chemistry - Question b - 2015
Question b
What is an exothermic reaction?
Name the instrument used to accurately measure the calorific values of different foods.
Define heat of combustion of a substance.
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Worked Solution & Example Answer:What is an exothermic reaction?
Name the instrument used to accurately measure the calorific values of different foods - Leaving Cert Chemistry - Question b - 2015
Step 1
What is an exothermic reaction?
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Answer
An exothermic reaction is a chemical reaction that releases heat energy to the surroundings. This process results in a temperature increase of the surrounding environment.
Step 2
Name the instrument used to accurately measure the calorific values of different foods.
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Answer
The instrument used to accurately measure the calorific values of different foods is called a calorimeter.
Step 3
Define heat of combustion of a substance.
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Answer
The heat of combustion of a substance is the amount of heat energy released when one mole of that substance is completely burned or oxidized in excess oxygen.
Step 4
Calculate the heat of combustion of hexane.
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The heat of combustion per mole of hexane can be calculated from the overall reaction:
Given that for 2 moles of hexane the heat released is -8326 kJ, therefore for 1 mole:
rac{-8326 ext{ kJ}}{2} = -4163 ext{ kJ mol}^{-1}
Step 5
Is this reaction exothermic? Give a reason for your answer.
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Answer
Yes, this reaction is exothermic. The value of ΔH is negative, indicating that heat is released. All combustion reactions are exothermic, and specifically, hexane is a fuel that releases energy upon combustion.
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