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• Power


  The rate at which energy is transferred
• Power


  The rate at which work is done
• Calculating power (energy transfer)

  Energy transferred / Time taken
• Calculating power (work done)


  Work done / Time taken
• Work done is a special measure of energy transferred when a force is used to move an object by a certain distance
• Energy transferred and work done are measured in joules, time is measured in seconds, and power is measured in watts
• Comparing two lamps


  • Lamp 1: 1200 joules over 20 seconds
  • Lamp 2: 1500 joules over 30 seconds
• Lamp 1 transfers 1200 joules over 20 seconds


  Power = 1200 joules / 20 seconds = 60 watts
• Lamp 2 transfers 1500 joules over 30 seconds

  Power = 1500 joules / 30 seconds = 50 watts
• Lamps may have a label indicating their power
• Calculating energy transferred by a 1100 watt microwave in 3 minutes


  Power x Time = 1100 watts x 180 seconds = 198,000 joules = 198 kilojoules
• Calculating power used to push a car 9 kilojoules over 20 seconds


  Work done / Time taken = 9000 joules / 20 seconds = 450 watts
• Chemical Equation


  A way to show a chemical reaction
• Word Equation


  • Shows the reactants and products using words, but doesn't show what happens to the atoms
• Symbol Equation


  • Shows the reactants and products using chemical symbols and formulas, and shows what happens to the atoms
• Balancing a Chemical Equation

  1. There must always be the same number of atoms of each element on both sides of the equation

  2. You balance the equation by putting numbers in front of the formulas where needed
• Balancing the equation: H2SO4 + NaOH → Na2SO4 + H2O


  • You're short of H atoms on the RHS, so make it 2H2O
  • But that now gives too many H atoms and O atoms on the RHS, so put a 2 in front of the NaOH on the LHS
• Balancing equations is all about practice
• Steps to balance an equation

  1. Find an element that doesn't balance

  2. Pencil in a number to try and sort it out

  3. See where it gets you, it may create another imbalance

  4. Pencil in another number and see where that gets you

  5. Carry on chasing unbalanced elements and it'll sort itself out