Question

2. Calculation of the atom economy of the reaction according to the following expression (8):

% Atom Economy = (Mol. Wt. of Product / S(Mol. Wt. of Reactants)) x 100

How might the atom economy be improved by changing the structure of one of the starting materials? Can you predict any drawbacks to doing this?

Answer 1

atom economy (a measure of atom utilisation or efficiency) is a measure of the amount of starting materials that end up as useful products. It is important for sustainable development and for good economic reasons to use reactions with high atom economy.

A chemical reaction may give, and often does, more than one product, but of the mixture of products, perhaps only one of them is the desired useful product.

The percentage atom economy of a reaction is readily calculated using the balanced equation for the reaction expressed in reacting masses.

You need to be able to calculate the atom economy of a reaction to form a desired product from the balanced equation and ...

perhaps explain why a particular reaction pathway is chosen to produce a specified product given appropriate information such as atom economy, percent yield, rate of reaction, equilibrium position and usefulness of by-products.

The atom economy of a reaction is a theoretical percentage measure of the amount of starting materials that ends up as the 'desired' useful reaction products. Its sometimes referred to as atom utilisation.

% Atom Economy = (Mol. Wt. of Product / S(Mol. Wt. of Reactants)) x 100

greater the % atom economy of a reaction, the more 'efficient' or 'economic' .In atom economy calculatins you can say REACTANTS or PRODUCTS because of the law of conservation of mass.

Many reactions give more than one product, and not all of them are useful, so it is useful to calculate what % of the products is theoretically useful, and we call this the atom economy of the reaction.

• The greater the value of the %atom economy, the less the amount of waste product produced.

• If one or more waste products are formed, the % atom economy is less than 100%.

  Some of the atoms present in the reacting molecules are converted into the desired product, the rest go into the formation of waste products.