5.5.1.1 Energy transfer during exothermic and endothermic reactions
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Law of conservation of energy states:
Energy cannot be created or destroyed.
Energy can only be transferred from one store to another.
Energy is conserved in any chemical reaction.
the amount of energy in universe
before the reaction takes place
=
the amount of energy in universe
at the end of a chemical reaction
In an exothermic reaction,
energy is transferred to the surroundings
so, the temperature of the surroundings (thermometer) will increase.
Examples of exothermic reactions:
Combustion (Oxidation)
Neutralisation (alkali + acid)
Metal + acid
Respiration
In an endothermic reaction,
energy is taken in from the surroundings
so, the temperature of the surroundings (thermometer) will decrease.
Examples of endothermic reactions:
Thermal decomposition (break down a carbonate using heat)
Citric acid + sodium hydrogen carbonate
Ammonium nitrate + water
Q1. What is the law of conservation of energy?
Energy cannot be created or destroyed.
Energy can only be transferred from one store to another.
Q2. What is an exothermic reaction?
A reaction where energy is transferred from the reaction to the surroundings.
Q3. What are two examples of exothermic reactions?
Combustion
Oxidation
Respiration
Neutralisation
Q4. What happens to the temperature of the surroundings during an exothermic reaction?
Increases
Q5. Give a real-life use of an exothermic reaction.
Handwarmers, self-heating cans
Q6. What is an endothermic reaction?
Q6. What is an endothermic reaction?
A reaction where energy is transferred from the surroundings into the reaction.
Q7. What are two examples of endothermic reactions?
Thermal decomposition reactions
Citric acid and sodium hydrogen carbonate
Ammonium nitrate + water
Q8. What happens to the temperature of the surroundings during an endothermic reaction?
Decreases
Q9. Give one real life use of an endothermic reaction.
Q9. Give one real life use of an endothermic reaction.
Sports injury cool packs
Q10. Is respiration an exothermic or endothermic reaction?
Exothermic
Q11. Is photosynthesis an exothermic or endothermic reaction?
Endothermic
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