Physical and chemical change

• What is a physical change?

  When a change undergoes a physical properties is known as physical change
• Examples of physical changes are boiling water, breaking a glass, melting an ice cube, freezing water, mixing sand and water, crumpling of paper.
• What is chemical change?

  A change in which one or more new substances are formed is called a chemical change.
• What is rust ? what is rusting?

  If you leave a piece of iron in the open for some time, it acquires a film of brownish substance. This substance is called rust and this process is called rusting
• What is physical properties?

  Properties such as shape, size, colour and state of a substance are

  called its physical properties
• What is essential for rusting?

  For rusting, the presence of both oxygen and water (or water vapour) is essential
• What is the equation for rusting?

  Iron (Fe) + Oxygen (O2, from the air) + water (H2O) -> rust (iron oxide Fe2O3)
• What is galvanisation?

  process of depositing a layer of zinc on iron is called galvanisation.
• What else can happen in chemical change?

  • Heat, light or any other radiation (ultraviolet, for example) may be given off or absorbed.
  • Sound may be produced.
  • A change in smell may take place or a new smell may be given off.
  • A colour change may take place.
  • A gas may be formed
• What is crystallization?

  large crystals of pure substances can be formed from their solutions. This process is called crystallization
• Cutting a log of wood into pieces is a chemical change. (True/False)

  False
• Iron pipes coated with zinc do not get rusted easily. (True/False)

  True
• Iron and rust are the same substances. (True/False)

  False
• When carbon dioxide is passed through lime water, it turns milky due to the formation of _________.

  Calcium carbonate
• The chemical name of baking soda is _________.

  Sodium hydrogencarbonate