GCSE OCR Gateway Chemistry C5.1i-j Atom Economy

GCSE OCR Gateway Chemistry C5.1i-j

C5.1i  

To be able to recall the definition of the atom economy of a reaction

C5.1j

To be able to calculate the atom economy of a reaction to form a desired product from the balanced equation

Atom Economy

These are days of conservation and green policies.  We recycle and conserve as much of our resources as we can.  Waste is a very dirty word no more so than in the chemical industry.

That’s the big picture into which the concept of atom economy fits very neatly.

These days all atoms in reactions can be useful and the more that are turned into useful products in a chemical change the better.  What atom economy measures is the percentage of reactant atoms turned into the desired and useful product.

In some reactions the determination of the percentage atom economy is very easy e.g. take the formation of ethanol from ethene and steam.

Here is the chemical equation:

C₂H₄     +    H₂O      ⟶       C₂H₅OH

As you can easily see, all the reactant molecules of ethene and steam are turned into ethanol: it is the only product according to this equation.

So the atom economy is 100%.

But what if you wanted to find the atom economy of carbon dioxide in the reaction between sodium carbonate and hydrochloric acid?

First, write down the chemical equation:

Na₂CO₃   +   2HCl      ⟶    2NaCl     +   H₂O     +   CO₂

Next, work out the relative masses of the reactants and the desired product:

Na₂CO₃   +   2HCl      ⟶    2NaCl     +   H₂O     +   CO₂

106                 73                                                            44

Next, apply the formula for atom economy:

Now you could work out what the atom economy is for the sodium chloride in the above reaction.