Energy changes and reversible reactions
Exothermic [exothermic: Heat energy is released in an exothermic reaction. We know this because the surroundings get warm. ] reactions transfer energy to the surroundings. Endothermic [endothermic: In an endothermic reaction, energy is taken in from the surroundings. The surroundings then have less energy than they started with, so the temperature falls. ] reactions take in energy from the surroundings.
Reversible reactions are where the productsproduct: A product is a substance formed in a chemical reaction. can react to remake the original reactantsreactants: substances present at the start of a chemical reaction. If the forward reaction is exothermic, the reverse reaction is endothermic.
When a chemical reaction occurs, energy is transferred to, or from, the surroundings - and there is often a temperature change. For example, when a bonfire burns it transfers heat energy to the surroundings. Objects near a bonfire become warmer. The temperature rise can be measured with a thermometer.
These are reactions that transfer energy to the surroundings. The energy is usually transferred as heat energy, causing the reaction mixture and its surroundings to become hotter. The temperature increase can be detected using a thermometer. Some examples of exothermic reactions are:
These are reactions that take in energy from the surroundings. The energy is usually transferred as heat energy, causing the reaction mixture and its surroundings to get colder. The temperature decrease can also be detected using a thermometer. Some examples of endothermic reactions are:
The animation shows an exothermic reaction between sodium hydroxide and hydrochloric acid, and an endothermic reaction between sodium carbonate and ethanoic acid.
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