Exothermic reaction — Science definition
Defined in 2 courses:
- A reaction that releases energy to its surroundings, usually warming them up. (Physical Science: Matter, Forces & Energy)
- A reaction that releases energy to its surroundings; its ΔH is negative and the surroundings warm up. (Physical Science: Chemistry)
Where it is taught
- Endothermic & Exothermic Reactions — Chemistry, Physical Science: Matter, Forces & Energy, Grade 8
- Energy in Chemical Reactions — Chemical Energy & Thermodynamics, Physical Science: Chemistry, Grade 11
In use
In an exothermic reaction, forming the new bonds releases more energy than breaking the old ones used up, so the leftover energy flows OUT into the surroundings — usually as heat, making everything nearby feel warmer.
Endothermic & Exothermic Reactions
An exothermic reaction has negative ΔH: the products have lower enthalpy than the reactants for the stated amounts and conditions.
Energy in Chemical Reactions
Questions using exothermic reaction
Problem 1
In an exothermic reaction, energy is…
- absorbed from the surroundings, cooling them
- released to the surroundings, warming them
- destroyed completely
- only stored, never released
Answer and explanation
released to the surroundings, warming them
Exothermic reactions release energy outward to the surroundings, which is why they feel warm.
Problem 2
An exothermic reaction
- absorbs energy from the surroundings
- releases energy to the surroundings
- neither absorbs nor releases
- destroys energy
Answer and explanation
releases energy to the surroundings
Exothermic reactions release energy, usually warming the surroundings.
Problem 3
On a potential-energy diagram for an exothermic reaction, the products are…
- at the same level as the reactants
- always at zero
- higher than the reactants
- lower than the reactants
Answer and explanation
lower than the reactants
An exothermic reaction releases energy, so the products end lower than the reactants and ΔH is negative.
Taught alongside
- endothermic reaction
- activation energy
- model
- evidence
- system boundary
- assumption
- enthalpy change (ΔH)
- bond energy
- activation energy (Ea)
- specific heat (c)