atom economy and percentage yield

• what is the percentage atom economy calculation?

  % atom economy = mass of desired products / total mass of reactants x100
• why is higher atom economy better?

  less waste materials
• example: calculate atom economy for NaOCl being produced from reaction of NaOH and Cl2 gas

  2NaOH + Cl2 --> NaCl + H2O + NaOCl

  Mr 40 71 58.5 18 74.5

  moles 2 1 1 1 1

  mass 20 71 58.5 18 74.5

  atom economy = 74.5 / (80+71) x100 = 49.3%
• what is the percentage yield calculation?

  percentage yield = actual mass of product / theoretical mass of product x 100
• what factors decrease yield?

  1. reaction doesn't go to completion
  2. reversible reaction
  3. impurities present
  4. secondary reaction occurs
  5. product lost in transfer
• example: 160g of PCl3 produced 100g of HCl, calculate percentage yield

  PCl3 + 3H2O --> H3PO3 + 3HCl

  moles of PCl3 - 160 / 137.5 = 1.164 moles

  moles of HCl - 1.164 x 3 = 3.4921 moles

  theoretical HCl mass - 3.4921 x 36.5 = 127.42g

  percentage yield - 100 / 127.42 x 100 = 78.48%