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Exothermic and endothermic reactions key terms
Use these key terms for Exothermic and endothermic reactions in AQA Chemistry 8462. The page is built from approved learning objectives for this topic and links back to the wider unit, topic hub, and related revision assets.
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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.
Collision theory
The theory that chemical reactions occur only when reacting particles collide with sufficient energy.
Activation energy
The minimum energy that reacting particles must possess for a chemical reaction to occur.
Collision theory
The theory that chemical reactions occur only when reacting particles collide with sufficient energy.
Activation energy
The minimum energy that reacting particles must possess for a reaction to occur. In Reaction profiles, this term is used specifically to support the learning objective: explain that reacting particles must collide with sufficient energy for a reaction to occur.
Activation energy
The minimum energy particles need to react. In Reaction profiles, this term is used specifically to support the learning objective: define activation energy as the minimum energy particles need to react.
Reaction profile
A graphical representation showing the energy changes during a chemical reaction. In Reaction profiles, this term is used specifically to support the learning objective: define activation energy as the minimum energy particles need to react.
Exothermic Reaction
A reaction that transfers energy to the surroundings, resulting in an increase in the temperature of the surroundings.
Reaction Profile
A graphical representation showing the energy changes during a chemical reaction, indicating the energy of reactants and products.
Reaction profile
A graph showing the change in energy of a reaction system as the reaction proceeds, with reactants, products, activation energy, and overall energy change marked.
Endothermic reaction
A reaction that absorbs energy from the surroundings, resulting in a higher energy state for the products than for the reactants.
Reactants
The substances present at the start of a chemical reaction, shown at the left side of a reaction profile.
Products
The substances formed after a chemical reaction, shown at the right side of a reaction profile.
Activation energy
The minimum energy particles need to react. In Reaction profiles, this term is used specifically to support the learning objective: label activation energy on a reaction profile.
Reaction profile
A graphical representation showing the energy changes during a chemical reaction. In Reaction profiles, this term is used specifically to support the learning objective: label activation energy on a reaction profile.
overall energy change
The difference in energy between the reactants and products in a chemical reaction, indicating whether energy is absorbed or released.
reaction profile
A graphical representation showing the energy changes during a chemical reaction, including the energy of reactants, products, and activation energy.
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, resulting in a decrease in the temperature of the surroundings.
Reaction profile
A graph showing the energy of reacting particles over time, with a curved line indicating how energy rises to a peak (activation energy) and then falls as products form.
Curved line
The continuous part of a reaction profile that represents the gradual change in energy of the system as the reaction proceeds from reactants to products.
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, resulting in a decrease in the temperature of the surroundings.
Bond breaking
The process of supplying energy to overcome the forces holding atoms together in a molecule.
Exothermic reaction
A chemical reaction that releases energy to the surroundings, resulting in an increase in temperature.
Bond formation
The process in which energy is released when chemical bonds are created between atoms in products.
Exothermic reaction
A chemical reaction that releases energy to the surroundings, resulting in an increase in temperature.
Bond energy
The amount of energy required to break one mole of a specific bond in a molecule. In The energy change of reactions (HT only), this term is used specifically to support the learning objective: (HT only) Explain that bond energies can be used to calculate energy needed to break bonds.
Exothermic reaction
A reaction that transfers energy to the surroundings, resulting in an increase in temperature.
Bond energy
The energy required to break one mole of a bond in a substance. In The energy change of reactions (HT only), this term is used specifically to support the learning objective: (HT only) Explain that bond energies can be used to calculate energy released when bonds form.
Energy released
The energy that is given off when bonds are formed in a chemical reaction. In The energy change of reactions (HT only), this term is used specifically to support the learning objective: (HT only) Explain that bond energies can be used to calculate energy released when bonds form.
Bond energy
The energy required to break one mole of a specific bond in a molecule. In The energy change of reactions (HT only), this term is used specifically to support the learning objective: (HT only) Calculate the total energy needed to break bonds in reactants from supplied bond energies. (MS 1a).
Exothermic reaction
A reaction that transfers energy to the surroundings, resulting in an increase in temperature.
bond energy
The average energy required to break one mole of a specific type of bond in a molecule. In The energy change of reactions (HT only), this term is used specifically to support the learning objective: (HT only) Calculate the total energy released when bonds form in products from supplied bond energies. (MS 1a).
energy released
The energy that is emitted when bonds are formed in the products of a chemical reaction.
overall energy change
The difference between the energy needed to break bonds in reactants and the energy released when bonds form in products.
bond energy
The amount of energy required to break one mole of a specific bond in a molecule. In The energy change of reactions (HT only), this term is used specifically to support the learning objective: (HT only) Calculate the overall energy change as energy needed to break bonds minus energy released when bonds form.
exothermic reaction
A reaction that transfers energy to the surroundings, resulting in an increase in the temperature of the surroundings.
bond energy
The energy required to break one mole of a specific bond in a molecule, which can be used to determine whether a reaction is exothermic or endothermic.
Endothermic reaction
A reaction that takes in energy from the surroundings, resulting in a decrease in temperature.
Bond energy
The energy required to break one mole of bonds in a substance, which influences whether a reaction is endothermic or exothermic.
bond energy
The average energy required to break one mole of a specific type of bond in a molecule. In The energy change of reactions (HT only), this term is used specifically to support the learning objective: (HT only) Use supplied bond energy data to calculate the energy transferred in a chemical reaction.
energy transfer
The movement of energy from one system to another, often observed as heat in chemical reactions.
energy transfer
The movement of energy from one system to another, which can be measured in chemical reactions.
enthalpy change
The heat content change of a system at constant pressure, often represented as ΔH in chemical reactions.
Bond energy calculation
A quantitative method that uses the energies required to break bonds in reactants and the energies released when bonds form in products to determine the overall energy change of a reaction.
Reaction profile interpretation
A qualitative analysis of a plotted energy diagram that identifies whether a reaction is exothermic or endothermic by comparing the relative energies of reactants, products, and the activation energy.
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