It is important for sustainable development and for economic reasons to…

The idea

Choosing reactions with high atom economy supports sustainable development because fewer reactant atoms are wasted as by-products, so less raw material is consumed and less waste must be treated or disposed of. There are also economic benefits: raw materials cost money, and separating, purifying and disposing of unwanted by-products adds further cost and energy use. A process that converts most of its starting materials into the desired product uses resources more efficiently, produces less waste and is often cheaper to run. For example, an addition reaction that gives a single product avoids the cost of separating a mixture and the cost of disposing of a co-product. However, atom economy is only one factor; a company must also consider yield, rate, equilibrium position, energy demands, safety and the usefulness of any by-products before selecting a pathway.

What earns the marks

• Explain that high atom economy reduces waste because a greater proportion of reactant atoms become the desired product.
• Link high atom economy to sustainable development by describing reduced consumption of raw materials and reduced waste disposal.
• Link high atom economy to economic benefits such as lower raw material costs and lower separation, purification and disposal costs.
• Recognise that atom economy is one of several factors, including yield, rate, equilibrium position and by-product usefulness, that influence pathway choice.
• Apply the argument to a specific reaction by identifying the by-product that would be avoided or the cost that would be reduced.

Common mistakes and how to put them right

• Claiming that high atom economy alone guarantees a profitable process.

  Put it right by stating that yield, rate, energy costs and equilibrium position must also be considered.

• Treating sustainability as only an environmental issue.

  Put it right by explaining that reducing waste and raw material use also lowers costs.

• Assuming all by-products are useless.

  Put it right by noting that a by-product may be sold or used elsewhere, which can make a lower atom economy pathway acceptable.

Exam tips

• Use the phrase sustainable development and then explain it in terms of conserving raw materials and reducing waste.
• Give both an environmental and an economic reason when a question asks why high atom economy is important.
• Refer to the specific by-product named or implied in the question rather than discussing waste in general terms.