Reactions and temperature changes
Energy is conserved in chemical reactions, so the total amount of 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. in the universe at the end of a reaction is the same as it was before the reaction.
When a chemical reaction happens, energy is transferred to or from the surroundings. When energy is transferred to the surroundings, this is called an Reaction in which energy is given out to the surroundings. The surroundings then have more energy than they started with so the temperature increases. reaction, and the temperature of the surroundings increases. Examples of exothermic reactions include:
- The process of burning by heat. reactions
- many The gain of oxygen, or loss of electrons, by a substance during a chemical reaction. reactions
- most The reaction between an acid and a base to form a salt plus water. reactions
Everyday uses of exothermic reactions include self-heating cans and hand warmers.
When energy is taken in from the surroundings, this is called an Reaction in which energy is taken in. reaction and the temperature of the surroundings decreases. Examples of endothermic reactions include:
- Type of reaction in which a compound breaks down to form two or more substances when it is heated. reactions
- the reaction of citric acid and sodium hydrogencarbonate
Everyday uses of endothermic reactions include instant ice packs which can be used to treat sports injuries.
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. In exothermic reactions, energy exits.
A study of the energy changes involved in chemical reactions, whether exothermic or endothermic