Chemistry 2 physical and chemical changes

• Element


  a substance that contains only one type of atom all of the atoms in an element are the same elements are found on the periodic table
• Compound


  A substance made up of atoms of 2 or more different elements that are chemically bonded together. the elements bond in fixed ratios and can be shown with a chemical formula
• Mixture


  An impure substance made from 2 or more different elements or and compounds that are mixed together but not chemically joined. elements become chemically bonded because some elements are unstable by themselves so they join to other atoms so that the can get more energy so that they can start reacting
• A mixture is a combination of two or more pure substances in which each substance retains its own chemical identity
• Pure substance


  A single substance on its own
• Physical Changes


  1. No new substance is produced

  2. Change of state (e.g. solid to liquid)

  3. Particles are chemically bonded together in the same arrangement, just behaving differently

  4. Same number of atoms at the end as at the start
• Chemical Changes


  1. New substances are produced

  2. Atoms become chemically bonded together in a new arrangement

  3. Same number of atoms at the end as at the start, just chemically bonded in new arrangements
• The Law of Conservation of Mass states that in a chemical reaction no mass is lost or gained because atoms cannot be created or destroyed
• In a chemical reaction, the total mass of reactants equals the total mass of products
• Ways to tell a chemical reaction is occurring

  • Effervescence (fizzing, making bubbles)
  • Powder disappearing
  • Precipitation forming
  • Temperature change
  • New substance formed
  • Gas being released
• Exothermic reaction


  Involves an increase in temperature as heat energy is released
• Endothermic reaction


  Involves a decrease in temperature as heat energy is absorbed
• label the arrangements of particles

  A) pure compound - gas

  B) gaseous element

  C) mixture of gases

  D) liquid element

  E) liquid mixture

  F) solid compound

  G) solid element