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Exothermic and endothermic reactions key terms
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key terms
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Exothermic and endothermic reactions
Key terms
Energy conservation
The principle that energy cannot be created or destroyed, only transformed from one form to another in chemical reactions.
Chemical reaction
A process that involves the rearrangement of the molecular or ionic structure of a substance, resulting in the formation of new substances.
Exothermic reaction
A reaction that transfers energy to the surroundings, resulting in products with less energy than the reactants.
Endothermic reaction
A reaction that takes in energy from the surroundings, resulting in products with more energy than the reactants.
Exothermic reaction
A reaction that transfers energy to the surroundings. In Energy transfer during exothermic and endothermic reactions, this term is used specifically to support the learning objective: define an exothermic reaction as one that transfers energy to the surroundings.
Surroundings
The environment around a chemical reaction where energy transfer occurs. In Energy transfer during exothermic and endothermic reactions, this term is used specifically to support the learning objective: define an exothermic reaction as one that transfers energy to the surroundings.
Exothermic reaction
A reaction that transfers energy to the surroundings, resulting in an increase in the temperature of the surroundings.
Surroundings
The environment outside the reacting substances that can absorb or release energy during a chemical reaction.
Exothermic reaction
A reaction that transfers energy to the surroundings, resulting in an increase in temperature.
Combustion
A type of exothermic reaction that involves the burning of a substance in oxygen. In Energy transfer during exothermic and endothermic reactions, this term is used specifically to support the learning objective: identify combustion, many oxidation reactions and neutralisation as examples of exothermic reactions.
Self‑heating can
A container that releases heat to warm its contents, using an exothermic reaction such as the oxidation of iron powder.
Hand warmer
A small, disposable packet that generates heat through an exothermic reaction, typically involving the oxidation of iron powder and salt.
Endothermic reaction
A chemical reaction that absorbs energy from the surroundings, resulting in a lower temperature of the surroundings.
Surroundings
Everything external to the reacting system that can exchange energy with it. In Energy transfer during exothermic and endothermic reactions, this term is used specifically to support the learning objective: define an endothermic reaction as one that takes in energy from the surroundings.
Endothermic reaction
A reaction that takes in energy from the surroundings, resulting in a decrease in the temperature of the surroundings.
Surroundings
The environment outside of a chemical reaction where energy transfer occurs, affecting temperature changes.
Endothermic reaction
A reaction that takes in energy from the surroundings. In Energy transfer during exothermic and endothermic reactions, this term is used specifically to support the learning objective: identify thermal decomposition and the reaction of citric acid with sodium hydrogencarbonate as examples of endothermic reactions.
Thermal decomposition
A type of endothermic reaction where a compound breaks down into simpler substances when heated.
Endothermic reaction
A reaction that takes in energy from the surroundings. In Energy transfer during exothermic and endothermic reactions, this term is used specifically to support the learning objective: describe sports injury packs as an everyday use of endothermic reactions.
Sports injury pack
A practical application of an endothermic reaction used to reduce swelling and pain.
Exothermic reaction
A reaction that transfers energy to the surroundings, resulting in an increase in the temperature of the surroundings.
Endothermic reaction
A reaction that takes in energy from the surroundings, leading to a decrease in the temperature of the surroundings.
Exothermic reaction
A reaction that transfers energy to the surroundings, resulting in an increase in temperature.
Endothermic reaction
A reaction that takes in energy from the surroundings, resulting in a decrease in temperature.
Temperature change
The difference in temperature observed when substances react or dissolve in water.
Reactants
The starting substances that undergo a chemical reaction. In Energy transfer during exothermic and endothermic reactions, this term is used specifically to support the learning objective: describe how to measure temperature changes when substances react or dissolve in water. (AT 5).
Temperature change
The difference in temperature observed in the surroundings when a reaction occurs, indicating energy transfer.
Reaction variables
Factors such as concentration, type of reactants, and surface area that influence the magnitude of temperature change in a chemical reaction.
enthalpy change
The heat change associated with a chemical reaction at constant pressure. In Energy transfer during exothermic and endothermic reactions, this term is used specifically to support the learning objective: explain why calculation of enthalpy change or ΔH is not required for this GCSE section.
ΔH
The symbol representing the change in enthalpy during a reaction. In Energy transfer during exothermic and endothermic reactions, this term is used specifically to support the learning objective: explain why calculation of enthalpy change or ΔH is not required for this GCSE section.
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