Moles

• The symbol for the unit mole is mol
• The mass of one mole of a substance is numerically equal to its relative formula mass
• One mole of a substance contains the same number of particles as one mole of any other substance. - Avagadro's number which = 6.02 x 10^23
• Moles = mass / Ar or mass / Mr
• Mole equation triangle

  
• What is a limiting reactant?


  The reactant that get used up first in a reaction
• Why does the reactant get used up first in a reaction?

  Because it limits the amount of product that can be produced. This is the reactant that is not in excess . The reaction stops when the limiting reactant has been used up
• Exam style question - A company combusts 1000g of methane. How much water is produced in the reaction?


  Step 1 = Write out the balanced chemical equation

  CH(4) + 20(2) -> 2H(2)O + CO(2)

  1000g ?g

  Mr = 16 Mr = 18

  Step 2 = Highlight the substances that you are interested in + add information that you know about them ( Etc - Mr )
• Exam style question - A company combusts 1000g of methane. How much water is produced in the reaction?

  Step 3 = Calculate the moles of methane

  Moles of CH4 = mass ÷ Mr = 1000g ÷ 16 = 62.5mol

  Step 4 = Work out how many moles of water will be produced

  Moles water/moles methane = 2/1. So moles of water = 2x moles methane = 62.5 x 2 = 125mol
• Exam style question - A company combusts 1000g of methane. How much water is produced in the reaction?


  Step 5 = work out the mass of water

  Mass = moles x Mr

  Mass = 125mol x 18 = 2,250gH2O