Bond energies for some single and multiple bonds

• Resources Structure
• Key Stage 4
• Chemistry
• XIII. Chemical reactions
• 63. Endothermic and exothermic reactions

• Exam Specifications
• Key Stage 4
• AQA GCSE Science A (4461) Chemistry
• III. Additional materials
• 1. Additional materials
• Additional materials
• AQA GCSE Additional Science (4463) Chemistry
• I. Chemistry 2
• 5. Do chemical reactions always release energy?
• When chemical reactions occur, energy is transferred to or from the surroundings.
• An exothermic reaction is one that transfers energy, often as heat, to the surroundings. Examples of exothermic reactions include combustion, many oxidation reactions and neutralisation.
• An endothermic reaction is one that takes in energy, often as heat, from the surroundings. Endothermic reactions include thermal decompositions.
• AQA GCSE Chemistry (4421)
• II. Chemistry 2
• 20. Do chemical reactions always release energy?
• When chemical reactions occur, energy is transferred to or from the surroundings.
• An exothermic reaction is one that transfers energy, often as heat, to the surroundings. Examples of exothermic reactions include combustion, many oxidation reactions and neutralisation.
• An endothermic reaction is one that takes in energy, often as heat, from the surroundings. Endothermic reactions include thermal decompositions.
• III. Chemistry 3
• 25. How much energy is involved in chemical reactions?
• In an exothermic reaction, the energy released from forming new bonds is greater than the energy needed to break existing bonds.
• In an endothermic reaction, the energy needed to break existing bonds is greater than the energy released from forming new bonds.
• During a chemical reaction: − energy must be supplied to break bonds − energy is released when bonds are formed. These changes can be represented on an energy level diagram.

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