SC19

• Exothermic - energy is released to the surroundings, typically as heat which increases external temperature (e.g. combustion)
• Endothermic - energy is absorbed from the surroundings, typically as heat which decreases external temperature (e.g. melting ice)
• Exothermic Reaction Profile:

  • products are at a lower energy than the reactants
  • height difference shows energy given out
• Endothermic Reaction Profile:

  • products are at a higher energy than the reactant
  • height difference shows energy taken in
• Activation Energy - the minimum amount of energy needed for bonds to break
• Dissolving Salts in Water - add salt to a polystyrene cup of water then measure the temperature change once it is dissolved

  • dissolving ammonium chloride decreases temperature so it's endothermic
  • dissolving calcium chloride increases temperature so it's exothermic
• Neutralisation Reactions - an acid and base reaction is typically exothermic

  • ethanoic acid and sodium carbonate reaction is endothermic
• Displacement Reactions - more reactive element displaces a less reactive element which is usually exothermic
• Precipitation Reactions - two solutions mixed together to create a precipitate is usually exothermic
• During chemical reactions, old bonds are broken (endothermic) and new bonds are formed (exothermic).

  Therefore, a positive energy change is endothermic and a negative energy change is exothermic