Bitesize has changed! We're updating subjects as fast as we can. Visit our new site to find Bitesize guides and clips - and tell us what you think!
Print

Science

Percentage yield and atom economy

Page:

  1. 1
  2. 2
  1. Back
  2. Next

Atom economy

Atom economy is a way to measure the atoms wasted when making a chemical. The higher the atom economy, the 'greener' the process. 100 per cent atom economy means that all the atoms in the reactants have been converted to the desired product.

Calculating atom economy

Atom economy = Mr of desired productssum of Mr of all products × 100

For example, calculate the atom economy for making hydrogen by reacting zinc with hydrochloric acid: Zn + 2HCl → ZnCl2 + H2

Mr of H2 = 1 + 1 = 2

Mr of ZnCl2 = 65 + 35.5 + 35.5 = 136

Atom economy = 2136 + 2 × 100 = 2138 × 100 = 1.45%

Industrial processes - Higher tier

Industrial processes need as high an atom economy as possible, because this:

  • Reduces the production of unwanted products
  • Makes the process more sustainable [sustainable: Doing something in a way that minimises damage to the environment and avoids using up natural resources, eg by using renewable resources. ]

For example, hydrogen can also be made from methane and steam: CH4 + 2H2O → CO2 + 4H2

  • Mr of H2 = 1 + 1 = 2
  • Mr of CO2 = 12 + 16 + 16 = 44

Atom economy = 4 × 244 + (4 × 2) × 100 = 852 × 100 = 15.4%

Page:

  1. 1
  2. 2
  1. Back
  2. Next

Back to Chemical economics index

BBC © 2014 The BBC is not responsible for the content of external sites. Read more.

This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.