Observing change

• physical change. It describes a situation in which there is no

  change in particles, just the particle arrangement and energy.
• Chemical change - when a chemical reaction takes place and a new substance is formed.

  • during a chemical change energy can be released or absorbed.
  • ‘Chemical changes are hard to reverse
• The chemicals that react together are called reactants and the substances formed are called

  products. Chemical reactions are represented using equations (word equations and chemical

  equations).

  
• During a chemical reaction the atoms rearrange to form a new substance.

  • colour changes
  • Temperature changes
  • Light is emitted
  • bubbles of gas are produced
• Law of conservation of mass : The that the mass of a substance cannot be created or destroyed.

  • in physical and chemical changes there isn’t any change in the mass
• Mass :

  the mass of reactants = total mass of products
• A particle model diagram shows how particles (atoms) rearrange to form a new substance

  during a chemical reaction.
• How is it evident that mass is conserved - No change in the number/type of atom.
• When burning a match, a chemical reaction takes place and a new substance is formed, which cannot be reversed. (d) Gases produced:

  1. Carbon dioxide
  2. Water vapour