7.10 - Exothermic changes and reactions
Learn what exothermic means and how a temperature rise provides evidence of heat energy moving from a change or reaction to its surroundings.
Heat energy leaves the change
Exothermic change or reaction
An exothermic change or reaction gives out heat energy to the surroundings.
The surroundings include the water in a solution, the container and nearby air. When heat energy transfers to them, their temperature can rise. The reacting chemicals give out energy; the thermometer records the resulting temperature change.
For example, an activated hand warmer transfers heat energy to a hand. A neutralisation reaction can warm the solution in its cup. Exothermic also describes physical changes that give out heat, such as water freezing. It describes the direction of energy transfer, not whether a new substance forms.
“Gets hot” is an observation rather than a definition. A material can also get hotter because a heater supplies energy to it. To identify an exothermic change, link the warming to heat energy given out by the change itself.
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