Exothermic and endothermic reactions
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Flip to reveal answersWhat is enthalpy change, ΔH?
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All 12 Flashcards — Exothermic and endothermic reactions
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Question
What is enthalpy change, ΔH?
Answer
The **heat energy** released or absorbed by a reaction at **constant pressure** (units: kJ mol⁻¹).
Question
What is an exothermic reaction?
Answer
A reaction that **releases** energy to the surroundings, so they get **hotter**; **ΔH is negative**.
Question
What is an endothermic reaction?
Answer
A reaction that **absorbs** energy from the surroundings, so they get **colder**; **ΔH is positive**.
Question
Sign of ΔH for exothermic vs endothermic?
Answer
Exothermic → **ΔH < 0** (negative); endothermic → **ΔH > 0** (positive).
Question
Is breaking bonds endo- or exothermic?
Answer
**Endothermic** — energy must be **put in** to break a bond.
Question
Is making bonds endo- or exothermic?
Answer
**Exothermic** — energy is **released** when a new bond forms.
Question
When is a reaction overall exothermic?
Answer
When **making** the new bonds releases **more** energy than **breaking** the old bonds absorbed (net energy out).
Question
What is activation energy, Eₐ?
Answer
The **minimum** energy reactants need to react — the reactant level up to the **peak** of the profile.
Question
How do you read ΔH off an energy profile?
Answer
It is the energy gap between the **reactant** and **product** levels (down for exothermic, up for endothermic).
Question
Which products are more stable, exo or endo?
Answer
**Exothermic** products are **lower** in energy and so **more stable** than the reactants.
Question
Surroundings cool down — what type of reaction?
Answer
**Endothermic** — energy is absorbed from the surroundings, so **ΔH is positive**.
Question
Two examples of exothermic reactions?
Answer
**Combustion** and **neutralisation** (also respiration) — they release energy.
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Full study notes for Exothermic and endothermic reactions
Topic 4.1 hub
Measuring enthalpy change
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