Chemical reactions

• Physical change

  A change that does not alter the particles of the substances involved
• Chemical change

  A change that produces new substances
• Chemical reactions produce new products
• Chemical reactions


  Reactants rearranged to form products
• Examples of physical properties

  • Density
  • Ductility
  • Conductivity
  • Melting points
  • Boiling points
• Chemical property


  A property that can be identified only during a chemical change
• During a chemical reaction, substances change into different substances
• Cooking and burning produce different substances
• Examples of chemical properties

  • Flammability
  • Acidity
  • Toxicity
  • Reactivity
  • Stability
• During a chemical reaction, new substances are formed
• Reactants are the materials we start with in a chemical reaction
• Products are the new materials that form in a chemical reaction
• During a chemical reaction, no atoms are lost or destroyed
• Combustion reactions produce a lot of thermal energy
• Hydrogen is a fuel
• Methane is commonly known as 'natural gas'
• Burning is a combustion reaction
• Rust is the red-brown coating formed on iron and steel objects when exposed to damp conditions
• Reactions of metals with oxygen

  • Magnesium
  • Iron
• The general reaction of a metal reacting with oxygen is: metal + oxygen → metal oxide
• Metals of Group 1 react very fast with oxygen
• Some metals react vigorously with water
• Some metals do not react with water at all
• Metals that react with water produce heat, hydrogen gas, and the corresponding metal hydroxide
• When a metal reacts with an acid, the products formed are a salt and hydrogen gas
• Reaction of metals with acids

  Metal + acid → salt + hydrogen
• The production of hydrogen gas is a characteristic of the reaction of metals with acids
• Hydrogen is a colourless and odourless gas of low density
• The popping sound indicates the presence of hydrogen gas