Calculations, Moles and Yield


The Mole and Conservation of Mass

The Mole

  • amount of a substance
  • Avogadro's Constant 6x10(23)- how many particles
  • mass of atoms/molecules = same as relative atomic mass
  • number of moles= mass in g (of element)/mr (of element) 

Conservation of Mass

  • no atoms created/destroyed
  • same number/type of atom on each side
  • total mr of recatants=total mr of products
  • if mass changes it is because a gas (which was in the air), helps form the product making it heavier
  • if mass=smaller gas has escaped in reaction
1 of 4

Limiting Reactants

Reactions stop when a reactant is used up.

  • anything added in excess is to make sure the other reactant is used up
  • reactant thats used up=limiting reactant
  • half limiting reactant=half product- vice versa
  • product formed=directly proportional to amount of limiting reactant
  • to calculate mass of product:
  • balanced equation
  • work out Mr
  • (moles=mass/mr mass/mr)
2 of 4

Atom Economy

Atom economy=%of useful products

  • atom economy= mr of desired products/mr of reactants x100
  • 100% atom economy means all atoms in reactants turned into useful products
  • Problems:
  • low economy=onsume a lot of resources
  • waste (need to be disposed of) -expensive to do
  • not profitable
  • need to use waste products not throw away
3 of 4

Percentage Yield

Percentage yield compare actual+theoretical

  • %yield=mass of actual product/max theoretical mass product x100
  • high yield reduces waste and cost
  • yields are always less than 100%
  • not all reactants make a product (reversible reactions, can turn back
  • possible side reactions= extra product (react with air)
  • lose product when seperating from reaction mixture
4 of 4


No comments have yet been made

Similar Chemistry resources:

See all Chemistry resources »See all Calculations, moles and yield resources »