Exothermic and Endothermic Reactions

Exothermic and Endothermic Reactions

• Chemicals store a certain amount of energy, and different chemicals store different amounts of energy.
• If the products of a reaction store more energy than the original reactants, then they must have taken in the difference of temperature between the products and reactants from the surroundings during the reaction.
• But if they store less, then the excess energy is transferred to the surroundings during the reaction.
• The overall amount of energy doesn't change. This is because energy is conserved in reactions- it can't be created or destroyed, only moved around. This means the amount of energy in the universe always stays the same.
• An exothermic reaction is one in which energy is transferred to the surroundings, usually by heating. This is shown by a rise in temperature.
• The best example of an exothermic reaction is burning fuels- also called combustion. This gives out a lot of energy- it's very exothermic.
• Neutralisation equations (Acid + Alkali) are also exothermic.
• Many oxidation reactions are exothermic. For example, adding sodium to water releases energy, so it must be exothermic. The reaction releases energy and the sodium moves about on the surface of the water as it is oxidised.
• Exothermic reactions are used in hand warmers (iron + air + salt solution catalyst) to release energy, and in the bases of self heating cans.
• An endothermic reaction is one that takes in energy from the surroundings. This is shown by a fall in temperature.
• Endothermic reactions are much less common than exothermic reactions, but they include: thermal decomposition, and the reaction between citric acid and sodium…