chemical changes

• Physical Change:

  • Do not form new products
  • Energy may be taken in or given out
  • Usually easily reversible
• Chemical Change:

  • Form one or more new products
  • Matter interacts with heat, light, or electricity
  • Two or more different kinds of matter interact
  • Energy in the form of heat, light, or sound may be taken in or given out
  • Can be represented by word and chemical equation:

  Condition

  Reactant(s) → Product(s)

  (eg. heat, light)

  • Not easily reversible
• Interaction of substance(s) with Heat:

  • Combustion:

  → Occurs in the presence of heat and oxygen

  → Substance must be in direct contact with the flame (known as fuel)

  → Releases a lot of energy

  → Produces carbon dioxide and water (products) when complete combustion occurs

  Word equation:

  Carbon + Oxygen → Carbon dioxide + Water
• Interaction of substance(s) with Oxygen:

  • Combustion (explained in Heat)
  • Rusting:

  → Occurs when iron is exposed to moist air (where oxygen and water vapor is present) for some time

  → Red-brown substance is rust

  Word equation:

  Iron + Oxygen + Water → Rust
• Interaction of substance(s) with Oxygen:

  • Cellular respiration:

  → Living cells of plants and animals take in oxygen to release energy stored in glucose

  Word equation:

  Glucose + Oxygen → Carbon dioxide + Water
• Interaction of substance(s) with Light:

  • Photosynthesis:

  → Leaves make food in the presence of light

  → CO2 and H2O react in the presence of light and Chlorophyll to form glucose and oxygen

  Word equation:

  Sunlight + Carbon dioxide + Water → Glucose + Oxygen
• Interaction of substance(s) with Electric Current:

  • Electroplating:

  → Substance coated with metal with the passage of electric current

  → Prevents substance from rusting and corrosion
• Mixing Acids:

  • Have a sour taste
  • Change the color of indicators
  • Conduct electricity

  Examples of acids:

  • Hydrochloric acid
  • Citrus fruits (lemons, oranges)
  • Car batteries
• Mixing Alkali:

  • Have a bitter taste
  • Have a soapy feel
  • Change the color of indicators
  • Conduct electricity

  Examples of alkalis:

  • Sodium hydroxide
  • Soap bars
  • Baking soda
• Acids react with:

  • Reactive Metals:

  → Salt

  → Hydrogen

  • Carbonate:

  → Salt

  → Carbon dioxide

  • Alkalis (neutralization):

  → Salt

  → Water
• Chemical to Formulae to Remember:

  Acids:

  • HCl (hydrochloric acid)
  • HNO3 (nitric acid)
  • H2SO4 (sulfuric acid)

  Alkalis:

  • NaOH (sodium hydroxide)
  • KOH (potassium hydroxide)
  • NH3 (aqueous ammonia)
  • Ca(OH)2 (calcium hydroxide)

  (ALL ARE AQUEOUS!) (aq)
• State Symbols:

  Solid - (s)

  Liquid (melted) - (l)

  Gas - (g)

  Aqueous (solution) - (aq)
• Change of State ≠ Chemical Change
• Identify Presence of Hydrogen Gas:

  • Extinguished splinter with a pop sound
• Acid turn blue litmus paper red
• Alkali turn red litmus paper blue.
• a reaction between an acid and alkali is called neutralisation
• a white precipitate is formed when carbon dioxide is present in limewater
• bubbling is called effervescence
• oxidation occurs when

  oxygen is in the reactants