Everything you need to help your 14–16 learners with this tricky topic

Equilibrium is an important process in industry, eg for making ammonia using the Haber process which is a reversible reaction. Manufacturers want to make as much product as possible, minimising the quantity of starting materials left over. They also want to minimise energy use when conducting reactions at high temperatures and pressures.

To make reversible chemical reactions as efficient and sustainable as possible, manufacturers need to understand equilibrium. Because the equilibrium position – the concentrations of substances present at equilibrium – affects the yield of the product.

Reversible reactions

Most chemical reactions are irreversible, eg combustion, where the reaction only takes place in one direction. 

However, many chemical reactions are reversible: the products can react together to reform the original reactants. A reversible reaction is represented by a double arrow symbol: ⇌.

EiC-Equilibrium-Final-1

Source: © Dan Bright

Many chemical reactions are reversible: the products can react together to reform the original reactants. A reversible reaction is represented by a double arrow symbol: ⇌. The forwards reaction: A + B → C + D, and the reverse reaction: C + D → A + B, are occurring at the same time. If the forwards reaction is exothermic, the reverse reaction will be endothermic and vice versa. This is because the same amount of energy is transferred in both reactions

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Infographic poster, fact sheet and student worksheet. Display the poster in your classroom or on a projector. Alternatively, print it and use as a handout.

The accompanying storyboard activity asks learners to describe and sequence a dynamic equilibrium reaction using words and images.

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Two conical flasks containing a blue liquid - one is labelled open with arrows entering and leaving the flask and the other is labelled closed with a rubber bung preventing any particles entering or leaving the system

Source: © Dan Bright

Dynamic equilibrium can only happen in a closed system. This is a system or reaction vessel where nothing can enter or leave

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Did you know …?

In 2020, the Haber process – a reversible reaction – produced over 176 million tonnes of ammonia for fertiliser and other uses. 

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