Energy changes

• During a chemical reaction, energy transfers occur. Energy can be transferred to the surroundings (exothermic) or from the surroundings (endothermic)
• Energy is always conserved in chemical reactions, meaning that there is the same amount of energy in the universe at the start of a chemical reaction as at the end of one
• The activation energy is the minimum amount of energy required for particles to react when they collide.
• Oxidation, combustion and neutralisation are exothermic reactions
• Self heating cans and hand warmers are day to day examples of exothermic reactions
• In an exothermic reaction, more energy is released when making bonds than required to break bonds
• Thermal decomposition, citric acid and sodium hydrogen carbonate —> examples of endothermic reactions
• Sports injury packs are day to day examples of endothermic reactions
• Atoms are held together by strong chemical bonds. In a reaction, these bonds are broken and new ones are made between different atoms
• Breaking bonds requires energy and is therefore endothermic. Making bonds releases energy and is therefore exothermic
• Bond energy is the energy required to break a bond or the energy released when a bond is made