Exothermic Reaction Examples in Chemistry

Start with the recap, study the fully worked examples, then use the practice problems to check your understanding of Exothermic Reaction.

This page combines explanation, solved examples, and follow-up practice so you can move from recognition to confident problem-solving in Chemistry.

Concept Recap

A chemical reaction that releases energy (usually as heat or light) to the surroundings, resulting in an increase in surrounding temperature and a negative enthalpy change (\Delta H < 0).

The reaction gives off heat—you can feel the surroundings get warmer as it proceeds.

Read the full concept explanation →

How to Use These Examples

  • Read the first worked example with the solution open so the structure is clear.
  • Try the practice problems before revealing each solution.
  • Use the related concepts and background knowledge badges if you feel stuck.

What to Focus On

Core idea: Products have less energy than reactants; the excess energy is released as heat or light.

Common stuck point: \Delta H is negative for exothermic reactions (energy leaves the system).

Sense of Study hint: When determining if a reaction is exothermic, check the sign of \Delta H. First observe if the surroundings warm up (energy released). Then look at the energy diagram — products should be lower than reactants. Finally, confirm that \Delta H is negative.

Worked Examples

Example 1

easy
Explain why burning methane (\text{CH}_4 + 2\text{O}_2 \rightarrow \text{CO}_2 + 2\text{H}_2\text{O}) is an exothermic reaction.

Solution

  1. 1
    In an exothermic reaction, the energy released when new bonds form in the products is greater than the energy required to break bonds in the reactants.
  2. 2
    The C–O and O–H bonds in \text{CO}_2 and \text{H}_2\text{O} are very strong, releasing more energy than is needed to break the C–H and O=O bonds.
  3. 3
    The excess energy is released as heat and light (\Delta H < 0).

Answer

\Delta H < 0 \quad\text{(exothermic)}
Exothermic reactions release energy to the surroundings. Combustion reactions are classic examples — the heat released is what makes fuels useful for energy production.

Example 2

medium
A reaction releases 890 kJ of heat per mole of methane burned. If 3.2 g of \text{CH}_4 is burned (M = 16\,\text{g/mol}), how much heat is released?

Practice Problems

Try these problems on your own first, then open the solution to compare your method.

Example 1

easy
A hand warmer packet heats up when activated. Is this an exothermic or endothermic process? Explain.

Example 2

easy
A reaction mixture causes the beaker and surrounding air to become warmer. Is the reaction exothermic or endothermic? Explain.
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Background Knowledge

These ideas may be useful before you work through the harder examples.

chemical reactionenergy