Atom economy

• What is atom economy

  tells you how wasteful the process is

  based on how much product is lost because of things like :

  reaction not completing or losses during collection and purification

  doesn't measure how wasteful the reaction is itself

  reaction that has 100% yield could still be very wasteful if a lot of the atoms from the reactants wind up in by product rather than the desired product
• Atom economy - def

  measure of the proportion of reactant atoms that become part of the desired product (rather than by product ) in the balanced chemical equation
• Calculating atom economy

  molecular mass of desired product

  ///////// x100

  sum of molecular masses of all products
• How to calculate atom economy

  find the molecular mass of products you are interested in add up the molecular masses of the products and put both of them into formula

  you should use the moles of each compound that is in the balanced equation eg 2H2 = 2 x (2 x 1)
• Addition reactions

  reactants combine to form a single product

  the atom economy for addition reactions is always 100% since no atoms is wasted
• substitution reactions

  some atoms from one reactant are swapped with atoms from another reactant

  always results in at least two products - desired products and at least one by-product.

  so atom economy of substitution reaction is always less than 100%
• Atom economy and Percentage yield

  measure different things

  so a reaction that has a high percentage yield might have really low atom economy
• Atom economy in industry

  companies in the chemical industry will often choose to use reactions with high atom economies

  high atom economy has environmental and economic benefits
• atom economy has environmental benefits

  reactions with low atom economies are less sustainable

  many raw materials are limited supply so it makes sense to use them efficiently so they last as long as possible also waste has to go somewhere - its better for the environment if there is less produced
• Atom economy has economic benefits

  a low atom economy means there is lots of waste produced

  it costs money to separate the desired products from the waste products and more money to dispose of the waste products safely so they do not harm the environment

  companies will usually have paid good money to buy the reactant chemicals

  It is a waste of money if a high proportion of them end up as useless product
• Alternative for low atom economy

  still be used as waste products can be sold and used for something else ( waste products like gases ,salts and acids can often be useful reactants for other reactions )