A reaction that transfers energy to the surroundings usually by heating, indicated by a rise in temperature
Examples are combustion, neutralisation reactions (acid + alkali) and oxidation reactions (sodium added to water)
Everyday examples are hand warmers and self-heating cans
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What is an Endothermic Reaction?
A reaction that takes in energy from the surroundings, indicated by a fall in temperature
Examples are reactions between citric acid and sodium hydrocarbonate, thermal decomposition
An everyday example is sports injury packs
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How are bonds formed and broken?
Energy must be supplied to break existing bonds in bond breaking (endothermic)
Energy is released when new bonds are formed in bond forming (exothermic)
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How do you calculate bond energies?
Find the energy required to break the original bonds
Find the energy released by forming the new bonds
Find the overall energy change for the reaction using the equation:
overall energy change = energy required to break bonds - energy released by forming bonds
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