C2.5 exothermic and endothermic reactions
- 1. C2.5 Exothermic and Endothermic Reactions
- 2. C2.5 Exothermic and endothermic reactions Chemical reactions involve energy transfers. Many chemical reactions involve the release of energy. For other chemical reactions to occur, energy must be supplied. BTEOTSSSBAT: Know the difference between endothermic and exothermic reactions Know some example of endothermic and exothermic reactions
- 4. What happens when a chemical reaction takes place? What happens to the bonds?
- 5. Exothermic Reaction • Exothermic reactions transfer energy to the surroundings. • The energy is usually transferred as heat energy, causing the reaction mixture and its surroundings to become hotter. • Can you think of any examples?
- 6. • Combustion (burning) • Many oxidation reactions, for example rusting • Neutralisation reactions between acids and alkalis • Hand warmers
- 8. Screaming jelly babies! potassium chlorate, a strong oxidising agent, rapidly oxidises the sugar in the jelly baby
- 9. https://www.youtube.com/watch?v=aC-KOYQsIvU Hot Ice: supersaturated sodium acetate
- 10. Endothermic Reaction • These are reactions that take in energy from the surroundings. • The energy is usually transferred as heat energy, causing the reaction mixture and its surroundings to get colder. • Can you think of any examples?
- 11. • The thermal decomposition of calcium carbonate • Sports injury cold packs
- 13. AQA Science © Nelson Thornes Ltd 2006 16 Thermal decomposition of marble? Endothermic
- 14. AQA Science © Nelson Thornes Ltd 2006 17 Combustion of methane? Exothermic
- 16. AQA Science © Nelson Thornes Ltd 2006 19 Neutralisation of an acid and an alkali? Exothermic
- 17. AQA Science © Nelson Thornes Ltd 2006 20 Rusting of iron? Exothermic
- 18. AQA Science © Nelson Thornes Ltd 2006 21 Thermal decomposition of copper carbonate? Endothermic
- 19. AQA Science © Nelson Thornes Ltd 2006 22 Respiration? Exothermic
- 20. A reusable hand warmer contains a solution of sodium acetate trihydrate. When the hand warmer is activated, the sodium acetate trihydrate crystallises and heat is released. The word equation for this reaction is shown below: 1. What type of reaction is this? (1 mark) i. Using the information above, explain why hand warmers that contain sodium acetate trihydrate are reusable. (2 marks) Exothermic The reaction is reversible. (1 mark) So the solid sodium acetate trihydrate that is formed when the hand warmer is activated can be converted back into sodium acetate trihydrate solution (1 mark).
- 21. ii. Suggest how the hand warmer could be reset after use, so that it is ready to be used again. Explain your answer. (2 marks) The conversion of sodium acetate trihydrate solution to solid sodium acetate trihydrate is exothermic, so the reverse reaction (the conversion of solid sodium acetate trihydrate back to sodium acetate trihydrate solution) must be endothermic (1 mark). This means the hand warmer could be reset by heating it (1 mark).
Editor's Notes
- #5: Bonds are broken – requires energy ENDOTHERMIC Bonds are made – releases energy EXOTHERMIC
- #6: Where does the energy come from?
- #14: Exothermic: sodium hydroxide and hydrochloric acid copper(ii) sulfate and powdered zinc Endothermic: citric acid and sodium hydrogencarbonate ethanoic acid and sodium carbonate water and ammonium nitrate
- #15: 1. The polystyrene cup insulates and prevents energy losses. Using a lid also prevents heat loss. 2. Using more concentrated solutions would make the temperature changes greater. 3. You could not use this apparatus because there is no solution present to absorb the energy produced (in the case of the exothermic reaction). (Also, the polystyrene cup would burn.) 4. If a reaction is exothermic overall then the amount of energy needed to break the bonds in the reactants is less than the amount of energy released when the bonds are made in the products.