Chemical Reactions Revision

Chemical Reactions Revision

• Physical vs. Chemical Changes:

  • Physical changes alter appearance but not the substance's makeup (e.g., melting ice, dissolving salt).
  • Chemical changes create new substances (e.g., burning wood, reacting magnesium with acid).

• Indicators of Chemical Change:

  • Production of light
  • Production of heat
  • Production of sound
  • Change in colour
  • Production of an odour
  • Formation of bubbles or gases
  • Formation of a precipitate (solid particles)

• Reactants and Products:

  • Reactants are the starting substances in a chemical reaction.
  • Products are the substances formed as a result of the reaction.

• Bond Changes in Reactions:

  • Chemical bonds between atoms are broken and reformed in different ways during reactions.

• Endothermic vs. Exothermic Reactions:

  • Endothermic: Reactions absorb heat from the surroundings (e.g., ice melting, photosynthesis, ice packs).
  • Exothermic: Reactions release heat to the surroundings (e.g., adding magnesium to acid, heat packs).

• Neutralization Reactions:

  • Acid + base → salt + water
  • Example: hydrochloric acid + sodium hydroxide → sodium chloride + water

• Acid-Metal Carbonate Reactions:

  • Acid + metal carbonate → salt + water + carbon dioxide
  • Example: citric acid + sodium bicarbonate → salt + water + carbon dioxide

• Acid-Metal Reactions:

  • Acid + metal → salt + hydrogen
  • Example: magnesium + hydrochloric acid → magnesium chloride + hydrogen

• Metal-Oxygen Reactions:

  • Metal + oxygen → metal oxide
  • Example: magnesium + oxygen → magnesium oxide

• Non-Metal-Oxygen Reactions:

  • Non-metal + oxygen → non-metal oxide
  • Example: carbon + oxygen → carbon dioxide

• Combustion Reactions:

  • Fuel + oxygen → carbon dioxide + water (or hydrocarbon + oxygen → carbon dioxide + water)