states that if a dynamic equilibrium is disturbed by changing the conditions, the equilibrium position ‘shifts’ to counteract the change.

occurs in a closed system when the forward and backward reactions of a reversible chemical reaction occur at the same rate; and the concentrations of reactants and products remain constant.

refers to the relative concentrations of reactants and products in a reversible reaction at equilibrium.

is the speed with which a chemical reaction takes place, measured by the amount of a reactant used or amount of product formed in a given time.

Factors affecting equilibrium

Combined science

Introduction to reversible chemical reactions

Chemical equilibrium

In the Rates and energy changes unit, pupils learned about how energy changes are always involved in reaction, along with a range of methods for measuring and comparing rates of reaction using properties of reactants and/or products.

This unit covers corrosion, prevention methods, and properties of alloys, ceramics, polymers, and metals. It explores industrial processes like the Haber process, fertiliser production, reaction rates, yields, atom economy, and the trade-offs involving conditions and equilibrium.

Industrial chemistry

One mole of any gas occupies the same {{}} under the same temperature and pressure conditions.

Changing the number of particles of gas in a fixed volume will change the conditions. Adding gaseous matter changes the {{}} as there are more particles colliding with the walls of the container.

equilibrium doesn't change because the number of atoms are equal on both sides

the equilibrium shifts to the left, where there are more gas molecules  

the equilibrium shifts to the right, where there are fewer gas molecules  

Consider the reaction CO(g) + 2H₂(g) ⇌ CH₃OH(g).
What happens when the pressure is increased?

CO would also escape, and the reaction would stop.

CO₂ is a greenhouse gas, which we want to avoid putting in the atmosphere.

The reaction would cool down and the iron product would become solid.

Consider: Fe₂O₃(s) + 3CO(g) →2Fe(l) + 3CO₂(g).
It would be easy to let the by–product escape, to shift the equilibrium to get the desired product, Fe. Why is this undesirable?

Because a reversible reaction has an exothermic and an endothermic direction.

Because reactions slow down or speed up when temperature is changed.

Because temperature affects the rate of reaction.

Why does temperature affect the equilibrium position?

a chemical which speeds up the rate at which equilibrium is achieved

the relative concentrations of reactants and products at equilibrium

the equilibrium position shifts to counteract a change in conditions

Match the following key terms to their definitions.

The concentrations of reactants and products remain constant.

The forward and backward reactions occur at the same rate.

Occurs in a closed system, where matter cannot enter or leave.

Requires a catalyst to get started, and high pressure and temperature.

Requires a reversible reaction, with conditions feasible for both directions.

Which of the following statements for a dynamic equilibrium are correct?

The backward reaction no longer takes place.

The concentration of product is changed – all of the ammonia is removed.

The reactants, hydrogen and nitrogen gas, escape into the environment.

The system is opened so that matter can leave.

The temperature is lowered so the forward reaction slows down a lot.

When ammonia is removed during the Haber process, which of the following changes occur to the dynamic equilibrium?

a state where the forward and backward reaction rates are equal

the speed of chemical reactions: amount of matter used/made over time

factors including temperature and pressure that affect reaction rate

the amount of reactant or product in a defined volume of space

Match the following key terms to their definition.

The Haber process requires iron and the Contact process requires vanadium. These substances speed up the reactions without being used up or changed. Different reactions require different {{}}.

Which of the following graphs would be an appropriate representation of rate of reaction vs. time, for a dynamic equilibrium?

By-products could be waste but they can sometimes be made profitable.

Gaseous reactants/products can be difficult to contain for reuse or removal.

High pressure and temperature require considerable/expensive safety measures.

Remaining reactants can be hard to isolate from the desired product.

Unreacted reactants are economically and environmentally disadvantageous.

Many reactions in industrial chemistry are reversible reactions that reach equilibrium. 100% of the desired product can never be achieved. Which of the following issues may be encountered?

Starter Quiz