8.2 - Enthalpy Changes

• examples of exothermic reactions

  burning

  respiration

  hot packs: CaO + H2O → Ca(OH)2
• enthalpy change for exothermic reactions

  negative

  system loses energy to surroundings so temperature goes up
• examples of endothermic reactions

  melting & vaporisation

  photosynthesis

  cold packs

  thermal decomposition
• enthalpy change for endothermic reactions

  positive

  products are at a higher energy level than reactants
• ways to represent enthalpy changes

  enthalpy level diagrams

  reaction profile diagrams
• enthalpy level diagrams

  shows relative energies of reactants & products

  difference is enthalpy change so shows the overall change in a reaction
• reaction profile diagrams

  shows enthalpy changes during a reaction

  includes activation energy