chemical changes

• conservation of mass

  mass cannot be created or destroyed during reactions
• mass of reactants = mass of products
• physical reactions are reversible
• chemical reactions are irreversible
• signs of a chemical reaction:

  • change in colour
  • change in state
  • change in temperature
  • fizzing
  • reactants are used up
  • new substance appear
• metals/acids: chemical reactions

  • fizzes
  • gas is released
  • colourless solution
  • reactants used up
• EXO-thermic reactions:

  • energy is transferred to the surroundings from the reaction
  • the temperature increases after the reaction
  • examples: neutralisation, hand warmers
• ENDO-thermic reactions:

  • energy is transferred from the surroundings to the reaction
  • the temperature decreases after the reaction
  • examples: ice packs, thermal decomposition
• thermal decomposition: type of reaction which uses heat to break things down