Fwtkekrhehfe

• Physical change


  No new substances are formed

  The changes can usually be reversed
• Physical change


  • Freezing
  • Evaporation
• Chemical change


  One of more new substances are formed

  Changes are usually not easily reversed
• Chemical changes


  • Cooking
  • Rusting
• Reactants


  Substances which react with each other
• Products


  New substances formed from the reactants
• Chemical reaction representation


  Word equations
• During a chemical reaction, there is a rearrangement of atoms
• Combustion


  A substance is heated in the presence of oxygen to form one or more new substances

  Heat and light are usually given out
• Oxidation


  A substance gains oxygen
• Thermal Decomposition


  Process in which a substance breaks down into two or more simpler substances upon heating
• Neutralisation


  Acid reacts with an alkali
• Characteristics of Acids


  • Sour taste
  • Sometimes rough
  • pH below 7
  • Turns blue litmus paper red
  • Reacts with metal, carbonate, alkali
• Characteristics of Alkalis


  • Bitter taste
  • Soapy feel
  • pH more than 7
  • Turns red litmus paper blue
  • Reacts with acid
• Universal Indicator


  A mixture of indicators
• Universal Indicator and acids


  Turns red
• Universal Indicator and alkalis


  Turns violet
• Salt


  A compound with a metal element
• Alkali + Acid


  Salt + Water
• Applications of Neutralisation


  • Antacids
  • Toothpaste
  • Neutralising soil
• Metal + Acid


  Salt + Hydrogen
• Hydrogen gas test


  Use lighted splint (will extinguish with a pop sound)
• Carbonate + Acid


  Salt + Water + Carbon dioxide
• Carbon dioxide gas test


  Use limewater (turns cloudy)
• How chemical changes occur


  • Mixing
  • Interaction with oxygen
  • Heating
  • Exposure to light
  • Using an electric current
• Cooking


  Causes chemical reactions in food

  Cooking makes nutrients easier to absorb from food
• Respiration


  Glucose molecules react with oxygen to produce carbon dioxide and water
• The energy released in each cell during respiration allows the cell to survive
• Decay


  Process of breaking down organic matter into simpler substances
• Decay allows nutrients to be returned to the environment
• Decay causes food to be spoiled
• Ways to slow down decaying


  • Vacuum sealing
  • Reducing humidity
• Rusting makes structures more fragile
• Ways to prevent rusting


  • Painting
  • Oiling
  • Galvanising
  • Drying
• We need energy from the combustion of fuels
• Combustion of fuels releases air pollutants into the atmosphere
• Slash-and-burn practices


  Removing of trees/forests
• Harmful effects of slash-and-burn practices


  • Smoke given off causes air pollution
  • Harmful health effects from inhaling smoke
  • Carbon dioxide causes ocean acidification
• Ocean acidification


  Large amount of carbon dioxide in the atmosphere dissolves in the ocean causing carbonic acid to be formed
• Problems caused by ocean acidification


  • Corals containing calcium carbonate react with acidic sea water
  • Fish and plants may die due to lower pH conditions