Physical and chemical changes

• Change


  The act of altering a substance. An event, NOT a trait. Before condition → After condition.
• Physical Change


  • Does not alter the chemical composition or identity of the substance, only the form
• Physical Changes


  • Melting ice (change in state or phase)
  • Freezing Kool-aid
  • Tearing paper
  • Boiling water (change in state or phase)
  • Stretching silly putty
  • Making a mixture (ex. Sugar water)
  • Unmixing a mixture (ex. sorting)
• Characteristics of Physical Changes

  • MELTING: Solid → Liquid, Shape, Temperature
  • FREEZING: Liquid → Solid, Shape, Temperature
  • VAPORIZATION: YOUR TURN?!?!
  • CRUSHING: YOUR TURN!?!?!
  • BREAKING: Shape, Any Others?!?!?!
  • CONDENSATION: Gas → Liquid, What else?!?!
• States of Matter


  The 3 main states of matter: solid, liquid, gas. Changes in state are physical changes (no change in composition). Temperature is caused by the vibrational (kinetic) energy of atoms or molecules. As temperature increases, 1) solids turn to liquids, and 2) liquids turn to gases.

  
• Changes of State


  PHASE CHANGE = Physical Changes

  From a: SOLID, To a: LIQUID, Phase Change: MELTING, Added or Subtracted Energy: ADDING HEAT/ENERGY

  From a: LIQUID, To a: SOLID, Phase Change: FREEZING, Added or Subtracted Energy: SUBTRACTING HEAT/ENERGY

  From a: GAS, To a: LIQUID, Phase Change: CONDENSATION, Added or Subtracted Energy: SUBTRACTING HEAT/ENERGY

  From a: LIQUID, To a: GAS, Phase Change: VAPORIZATION/ BOILING/ EVAPORATION, Added or Subtracted Energy: ADDING HEAT/ENERGY

  From a: SOLID, To a: GAS, Phase Change: SUBLIMATION, Added or Subtracted Energy: ADDING HEAT/ENERGY

  From a: GAS, To a: SOLID, Phase Change: SUBLIMATION, Added or Subtracted Energy: SUBTRACTING HEAT/ENERGY
• Chemical Change


  Does alter the chemical composition or identity of a substance and makes new substances
• Chemical Changes


  • Burning paper
  • Digesting food
  • Rotting
  • Iron reacting with oxygen gas
• Chemical Reaction


  A chemical change is also called a chemical reaction
• Evidence for Chemical Reaction

  • Evolution of light
  • Temperature Change
  • Formation of a new Gas/Bubbles
  • Color Changes
  • Formation of a solid precipitate
• Is it Physical or Chemical?

  Melting cheese (Physical)

  Burning wood (Chemical)

  Milk souring (Chemical)

  Wadding up paper (Physical)

  Bicycle rusting (Chemical)
• Physical Property


  Can be observed without changing the identity of the substance (color, texture, density, viscosity, change in state, solubility, malleability, mass, volume)
• Chemical Property


  Describes the ability of a substance to undergo changes in identity. A new substance is produced (reactivity, toxicity, pH, conductivity, tarnishing, fermenting, oxidation)
• Properties


  • viscosity (physical)

  reactivity (chemical)

  density (physical)

  solubility (physical)

  tarnishing (chemical)

  rusting iron (chemical)

  dissolving in water (physical)

  burning a log (chemical)

  melting wax (physical)

  grinding spices (physical)