Endothermic and exothermic reactions
When a chemical reaction happens, The capacity of a system to do work or the quantity required for mechanical work to take place. Measured in joules (J). For example, a man transfers 100 J of energy when moving a wheelbarrow. is transferred to or from the surroundings. For example, changes in heat energy happen in the following situations:
- The substance formed when the hydrogen ion in an acid is replaced by a metal ion.When a substance breaks up and mixes completely with a solvent to produce a solution. in water
- The reaction between an acid and a base to form a salt plus water. reactions
- A reaction that occurs when a more reactive element replaces a less reactive element in a compound.
- A reaction in which an insoluble solid is formed when certain solutions are mixed.
When these reactions happen in solution, there are How warm or cold something is. changes that can be observed. These can be measured using a An instrument used to measure temperature..
Reactions can be Reaction in which energy is taken in. or Reaction in which energy is given out to the surroundings. The surroundings then have more energy than they started with so the temperature increases.. The table shows some differences.
| Endothermic | Exothermic | |
| Heat energy | Taken in | Given out |
| Temperature of reaction mixture | Decreases | Increases |
| Heat energy | |
|---|---|
| Endothermic | Taken in |
| Exothermic | Given out |
| Temperature of reaction mixture | |
|---|---|
| Endothermic | Decreases |
| Exothermic | Increases |
The slideshow describes an exothermic reaction between dilute sodium hydroxide and hydrochloric acid, and an endothermic reaction between sodium carbonate and ethanoic acid.
Image caption, 1. Sodium hydroxide solution is poured into a beaker of hydrochloric acid which contains a thermometer showing room temperature
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In endothermic reactions, energy enters from the surroundings. In exothermic reactions, energy exits to the surroundings.
A study of the energy changes involved in chemical reactions, whether exothermic or endothermic
What an exothermic and an endothermic reaction is, and how temperature changes can be used to identify which reaction is which