Reactions and temperature changes
Energy is conserved in chemical reactions. The total amount of energy in the universe never changes. When a chemical reaction occurs, energy is transferred to or from the reaction’s immediate surroundings.
- in endothermic reactions, energy enters.
- in exothermic reactions, energy exits.
Exothermic reactions
An An exothermic reaction gives out energy, usually in the form of heat. reaction transfers energy to its surroundings. The temperature of its surroundings increases.
Exothermic reactions include:
- Combustion is the reaction in which a fuel reacts with oxygen producing oxides and releasing heat. reactions
- many The gain of oxygen, loss of hydrogen 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
Endothermic reactions
An An endothermic reaction takes in heat. reaction takes in energy from its surroundings. The temperature of its surroundings decreases.
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 ethanoic acid and sodium carbonate
An exothermic reaction between dilute sodium hydroxide and hydrochloric acid.
Image caption, 1. Sodium hydroxide solution is poured into a beaker of hydrochloric acid. Inside is a thermometer showing room temperature.
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