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Endothermic & Exothermic Reactions

Noadswood Science, 2012. Endothermic & Exothermic Reactions. Endothermic & Exothermic Reactions. To understand endothermic and exothermic reactions. Reactions. Most chemical reactions involve energy change – often this energy is in the form of heat: -

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Endothermic & Exothermic Reactions

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  1. Noadswood Science, 2012 Endothermic & Exothermic Reactions

  2. Endothermic & Exothermic Reactions • To understand endothermic and exothermic reactions

  3. Reactions • Most chemical reactions involve energy change – often this energy is in the form of heat: - • Exothermic reaction - energy is given out (temperature increases) • Endothermic reaction - energy is taken in (temperature decreases) • Exothermic - e.g. combustion of fuel (heat given out by the chemicals to the surroundings) • Endothermic - e.g. ice cube melting in your hand (heat taken away from the surroundings to the chemicals (which is why your hand feels cold when you hold an ice cube and it melts))

  4. Energy Energy Energy • Energy must be supplied to break bonds • Energy is released when new bonds are made • A reaction is exothermic if more energy is released than supplied • If more energy is supplied than is released then the reaction is endothermic

  5. Energy • Complete the exothermic and endothermic reactions – record your observations as your progress…

  6. Exothermic Reaction • Exothermic reaction – energy level diagram

  7. Exothermic Reaction • Exothermic reaction – energy level diagram

  8. Endothermic Reaction • Endothermic reaction – energy level diagram

  9. Summary • 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, e.g. • Burning • Neutralisation reactions between acids and alkalis • The reaction between water and calcium oxide • Endothermic reactions take in energy from the surroundings – the energy is usually transferred as heat energy, causing the reaction mixture and its surroundings to get colder, e.g. • Electrolysis • The reaction between ethanoic acid and sodium carbonate • Thermal decomposition of calcium carbonate in a blast furnace

  10. Summary • Exothermic reaction between sodium hydroxide and hydrochloric acid, and an endothermic reaction between sodium carbonate and ethanoic acid: -

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