C2(i) - Bonding and Reactions 15.

Atom Economy.

It's important in industrial reactions that as much of the reactants as possible get turned into useful products. This depends on the atom economy and the percentage yield of the reaction. 

"Atom Economy" % of Reactants Changed to Useful Products.

1) A lot of reactions make more than one product. Some of them will be useful, but others will just be waste, e.g when you make quicklime from limestone, you also get CO2 as a waste product.

2) The atom economy of a reaction tells you how much of the mass of the reactants ends up as useful products. Learn the equation:

Atom Economy = Total Mr of useful products / Total Mr of reactants x 100

Example: Hydrogen gas is made on a large scale by reacting natural gas (methane) with steam.

CH4(g) + H2O(g) ------> CO(g) + 3H2(g)

Calculate the atom economy of this reaction.

Answer:
1) Identify the useful product - that's the hydrogen gas.

2) Work out the Mr of reactants and the useful product:

CH4 = 12 + (4 x 11)  H2O = (2 x 1) + 16      3H2 = 3 x (2…