Gcse equilibrium 2025-2026 RGSHW

12. Devise an experiment to show that the reaction converting hydrated copper sulfate (blue solid) to anhydrous copper sulfate (white solid) and water is a reversible reaction.

Reaction: CuSO₄·5H₂O ⇌ CuSO₄ + 5H₂O

Step 1: Demonstrate the forward reaction (decomposition).

Place a sample of hydrated copper sulfate crystals in a test tube.

the crystals with a Bunsen burner.

Observation: The crystals will turn , and will be observed coming off.

This shows the conversion to anhydrous copper sulfate and water.

Step 2: Demonstrate the reverse reaction (rehydration).

Allow the white copper sulfate to cool.

Then, add a few drops of to the white solid using a dropping pipette

Observation: The white solid will turn again.

You may also observe that heat is released (the water turns to .

Step 3: Conclude reversibility.

Since the substance can be converted from blue hydrated copper sulfate to white anhydrous copper sulfate and back again, the reaction is .

Compound A is a dark brown gas.

Compound B is a colourless gas.

Two molecules of A combine to form one molecule of B in a reversible reaction.

2A ⇌ B

Dark brown colourless

You are given

a sealed glass tube containing an equilibrium mixture of A and B

a beaker

a kettle

some ice

At room temperature, the equilibrium mixture is a pale brown colour.

Devise an experiment to show how the position of equilibrium of this reaction is affected by temperature.

1. Note the colour at room temperature

METHOD OF HEATING AND COOLING

put tube into water (1) and observe the colour

then into cold (1) and observe the colour

OBSERVATIONS • colour goes AND colour goes lighter /

At the , base of the boiling tube the solid Ammonium chloride to form and hydrochloric acid.

At the top of the boiling tube the ammonia and react to form ammonium chloride.

Note that ammonium chloride is an ionic compound even though all of the elements are non-metals.

NH₄⁺ and Cl^-

Shifts in the equilibrium position.

a) Changing the concentration of a reactant

An increase in concentration of a reactant will cause equilibrium to shift to the (the product side).

This will oppose the change

This will the yield.

A decrease in concentration of a reactant will cause equilibrium to shift to the (the reactant side).

This will oppose the change.

This will the yield.

Shifts in the equilibrium position.

a) Changing the concentration of a product

An increase in concentration of a product will cause equilibrium to shift to the (the product side).

This will oppose the change

This will the yield.

A decrease in concentration of a reactant will cause equilibrium to shift to the (the reactant side).

This will oppose the change.

This will the yield.

Shifts in the equilibrium position.

a) Changing the Temperature

An increase in temperature will cause equilibrium to shift to the direction.

This will oppose the increase in temperature as energy taken in in the endothermic direction.

For a reaction (such as the Haber process where the reaction is exothermic in the forward direction) This will the yield

A decrease in temperature will cause equilibrium to shift to the direction. This will oppose the change.

This will the yield.

Shifts in the equilibrium position.

a) decreasing the concentration of a product

decrease in concentration of a will cause equilibrium to shift to the (the product side).

This will the yield.

The effect of changing pressure (affects gasses only).

The effect of changing pressure depends on the balanced equation.

An increase in pressure will shift equilibrium to the side with moles of gas.

A decrease in pressure will shift equilibrium to the side with moles of gas.

Haber process and pressure

Pressure

200 atmospheres pressure

higher pressure gives a yield of ammonia

too high a pressure causes risk of / high pressure costly to maintain

a high pressure will cause the to be higher

4 moles of gas become 2 (or moles of gas in products).

Temperature of 450 °C

A higher temperature the rate of reaction (more frequent and more forceful collisions)

However, The forward reaction is so a higher yield of ammonia requires a temperature.

Unfortunately if the temperature is low the rate of reaction to be too

The temperature is a compromise between rate (better at higher temperatures) and yield.(better at lower temperatures.

The reverse reaction is exothermic and an increase in temperature favours the direction.

Catalyst

iron catalyst

A catalyst up the reaction by providing an alternative pathway of activation energy.

an iron catalyst allows a lower temperature to be used (saving energy)

iron catalyst increases the rate of reaction equally in directions.

A catalyst does not change the position of equilibrium but does allow equilibrium to be reached more

N₂ + 3H₂ ⇌ 2NH₃

The reaction is exothermic in the forward direction

If Hydrogen is added equilibrium will shift to the

If f Nitrogen is added equilibrium will shift to the

If ammonia is added equilibrium will shift to the

If the pressure is increased the equilibrium will shift to the

If the temperature is increased the equilibrium will shift to the