atom economy and yield

• what is atom economy?

  a measure of the amount of starting materials that end up as useful products
• a lot of reactions form more than one product. some will be useful, but others will be...

  waste
• the atom economy of a reaction tells you...

  how much of the mass of the reactants is wasted when manufacturing a chemical and how much ends up as the desired product
• atom economy =


  (relative formula mass of desired products / sum of all relative formula masses of all reactants) x 100
• what does 100% atom economy mean?

  all the atoms in the reactants have been turned into useful (desired) products - the higher the atom economy, the 'greener' the process
• high atom economy is better for...


  profits and the environment
• reactions with low atom economy use up...


  resources very quickly
• the reactions with the highest atom economy have...

  one product
• the more products there are...

  the lower the atom economy is likely to be
• pros of high atom economy

  - uses fewer natural resources

  - produces less waste

  - better for the environment
• cons of low atom economy

  - inefficient and wasteful

  - expensive/not profitable as materials can be expensive
• how can you work around the cons of low atom economy?

  by finding a use for the waste products, sometimes requiring the products to made differently in order for the waste products to be useful
• percentage yield compares...


  actual and predicted yield
• yield


  the amount of product obtained in a chemical reaction
• the more reactants you start with, the ... the yield


  higher
• percentage yield does not depend on...

  the amount of reactants you start with, it is a percentage
• percentage yield =


  (mass of product actually made/maximum theoretical mass of product) x 100
• percentage yield is always between...

  0-100%
• 100% yield means...


  you got all the product you expected to get
• 0% yield means...


  no reactants were converted into product
• why is it impossible to get 100% yield?

  - not all reactants react to make a product

  - there might be side reactions

  - you lose some product when you separate it from the reaction mixture
• why don't all reactants make a product?

  the particles in a reaction may lack the necessary energy or correct orientation, meaning not all of them collide and react
• why do side reactions affect how much product is made?

  extra products other than the wanted ones may be made if they react with gases in the air or impurities in the reaction mixture
• why do you lose some product when you separate it from the reaction mixture?


  when filtering a liquid to remove solid particles, some liquid or solids are lost. you will also lose a bit of material when transferring it from one container to another