Energy Changes
Middle School
Definition
The absorption or release of energy during a chemical reaction. Exothermic reactions release energy, usually as heat, raising the temperature of the surroundings, while endothermic reactions absorb energy and feel cold.
Worked examples
Burning wood releases heat and light into the air, warming your hands by the fire.
This exothermic reaction releases energy, raising the temperature around it.
An instant cold pack absorbs heat when chemicals mix, making your skin feel cold.
This endothermic reaction absorbs energy from the surroundings, lowering temperature.
\(\)CH\(_4 + 2\)O\(_2 \)→\( \)CO\(_2 + 2\)H\(_2\)O\( + \)energy\(\)
Methane combustion is exothermic — energy appears on the product side.
Common mistakes
- Endothermic reactions feel hot because they absorb energy → Endothermic reactions feel cold because they absorb energy from surroundings Absorbing energy pulls heat away from your hand or the container, making it colder.
- All reactions release energy → Exothermic reactions release energy; endothermic reactions absorb it Some reactions need continuous energy input to proceed and leave surroundings colder.
- Temperature change tells you if a reaction happened, not the energy direction → Temperature rise means exothermic; temperature drop means endothermic The direction of heat flow directly indicates whether energy was released or absorbed.
Where you'll use it next
You'll apply energy changes when studying activation energy and reaction rates, calculating enthalpy in thermochemistry, and understanding energy diagrams and bond energies in advanced chemistry.
See also
Reviewed by Pat Cheng, M.Ed. — StudyPug Curriculum Lead · Last updated June 6, 2026