Make your own free website on Tripod.com

Physical & Chemical Properties


PHYSICAL PROPERTIES

CHEMICAL PROPERTIES

  • Colour
  • Melting Point
  • Boiling Point
  • Solubility
  • Hardness
  • Strength
  • Elasticity
  • Heat Conductivity
  • Electrical Conductivity
  • Ability to transmit light
  • Lustre ('shininess' or dullness)
  • Magnetic attraction
  • pH
  • Reaction with oxygen (flammability or corrosion)
  • Reaction with water
  • Reaction with acids and bases
  • Reaction with metals

Physical & Chemical Changes

  • Physical Change occurs when no new substance is made, and the change is usually easy to reverse.
  • Examples of a Physical Change - freezing water, melting ice, dissolving common salt in water
  • Chemical Change (or Chemical Reaction) occurs when a new substance is made, and often the change is difficult to reverse. A chemical change is also usually accompanied by a colour change, a different smell, a bright light, a popping sound, or some other feature that our senses can detect.
  • Examples of a Chemical Change - cooking a cake, cooking a roast chicken, burning wood
  • Writing Chemical Reactions
In a chemical change, reactant chemicals react to form product chemicals.
e.g. HCl + NaOH Changes NaCl + H2O
Reactants Changes Products

ENERGY AND CHEMICAL REACTIONS

  • Endothermic Reactions - These are reactions that take in energy in the reaction. (e.g. Cooking a cake requires the input of heat energy from the oven.)
  • Exothermic Reactions - These reactions give out energy (e.g. When explosives are lit, there is an overall release of energy.)

FACTORS AFFECTING CHEMICAL REACTIONS

  • Amount of Reagents - The more reagent chemicals there are, the faster the reaction occurs.
  • Concentration of Reagents - The more concentrated reagents are, the faster the reaction occurs.
  • Temperature - The higher the temperature, the faster the reaction occurs.
  • Surface Area - When reagent chemicals are in a powder form, they have a greater surface area to come in contact, and the reaction occurs faster.
  • Catalysts - Catalysts are chemicals that speed up chemical reactions. They are not part of the overall reaction, and are reformed when the reaction is complete. Catalysts reduce the amount of energy required to start a reaction.

TYPES OF CHEMICAL REACTIONS

  • COMBINATION
A combination reaction occurs when 2 or more reactants combine to make 1 product. Combustion and corrosion are two examples of combination reactions.
Example 1
Iron + Oxygen Changes Iron Oxide
Fe + O2 Changes FeO
Example 2
Magnesium + Oxygen Changes Magnesium oxide
Mg + O2 Changes MgO
  • DECOMPOSITION
A decomposition reaction occurs when 1 reactant breaks down into 2 or more products.
Example 1
Calcium carbonate Changes Calcium oxide + Carbon dioxide
CaCO3 Changes CaO + CO2
Example 2
Copper carbonate Changes Copper oxide + Carbon dioxide
CuCO3 Changes CuO + CO2
  • DISPLACEMENT
The 2 ions that make up each of the 2 reactants 'swap partners' to make 2 new products.
Example 1
Hydrochloric acid + Sodium hydroxide Changes Sodium chloride + Water
HCl + NaOH Changes NaCl + H2O
Example 2
Sodium carbonate + Copper sulphate Changes Sodium sulphate + Copper carbonate
Na2CO3 + CuSO4 Changes Na2SO4 + CuCO3

COMBUSTION

  • Combustion is the burning of a substance in oxygen.
  • Example of a Combustion Reaction
  • Carbon + Oxygen Changes Carbon dioxide
    C + O2 Changes CO2
  • The Combustion Triangle
  • For combustion to occur, there must be:
  1. Oxygen
  2. Fuel - something that can burn
  3. Ignition Temperature - sufficient heat to keep the reaction going

BALANCING CHEMICAL EQUATIONS

  • Reactants are the chemical that begin the reaction and are on the left hand side of the arrow.
  • Products are the chemicals produced from the reactants and are on the right hand side of the arrow.
  • Law of Conservation of Matter
  • 'In a chemical reaction, matter cannot be created nor destroyed, but can only be changed from one form to another.'
    This means that the number of each type of atom before the reaction must equal the number of each type of atom after the reaction.