What is a reversible reaction ?

A reversible reaction is one that can proceed in both directions. Products from the forward reaction can react to reform the original reactants in the reverse reaction. The symbol ⇌ is used in the equation.

True or False? When water is added to white anhydrous copper(II) sulfate, the colour change observed is irreversible.

False. The reaction is reversible. Anhydrous copper(II) sulfate absorbs water and turns blue. Heating the blue hydrated form drives off the water and restores the white anhydrous solid.

Anhydrous cobalt(II) chloride is ______ . When water is added, it turns ______ . This change can be reversed by ______ .

Anhydrous cobalt(II) chloride is blue . When water is added, it turns pink . This change can be reversed by heating .

Why can cobalt(II) chloride and copper(II) sulfate be used as chemical tests for water?

Both undergo a visible colour change when they absorb water. Cobalt(II) chloride turns from blue to pink; copper(II) sulfate turns from white to blue. These distinct colour changes confirm the presence of water.

In the reaction CuSO 4 + 5H 2 O ⇌ CuSO 4 .5H 2 O, the white anhydrous copper(II) sulfate turns ______ when it absorbs ______ of crystallisation.

In the reaction CuSO 4 + 5H 2 O ⇌ CuSO 4 .5H 2 O, the white anhydrous copper(II) sulfate turns blue when it absorbs water of crystallisation.

What is water of crystallisation ?

Water of crystallisation is water that is chemically included in the structure of a hydrated salt. It is represented by a dot in the formula, for example CuSO 4 .5H 2 O or CoCl 2 .6H 2 O.

What is the difference between a hydrated and an anhydrous salt?

A hydrated salt contains water of crystallisation chemically incorporated into its crystal structure. An anhydrous salt has had this water removed, usually by heating. The two forms are interconverted by a reversible reaction.

True or False? When explaining how increased concentration of a reactant affects an equilibrium system, it is correct to use collision theory.

False. For CIE O Level, equilibrium shift questions are answered using Le Chatelier's Principle — the system shifts in the direction that opposes the change. Simply stating that more collisions occur in one direction is not an accepted explanation.

What is dynamic equilibrium ?

Dynamic equilibrium is the state reached in a reversible reaction when the rate of the forward reaction equals the rate of the reverse reaction. The concentrations of reactants and products remain constant, but both reactions continue to occur.

What happens to the position of equilibrium if the concentration of a reactant is increased?

The position of equilibrium shifts to the right. By Le Chatelier's Principle, the system opposes the increase by converting more reactant into product until a new equilibrium is established.

Equilibrium can only be established in a ______ system, where no reactants or products can ______ .

Equilibrium can only be established in a closed system, where no reactants or products can escape .

True or False? Adding a catalyst to an equilibrium mixture shifts the position of equilibrium to the right, increasing the yield of products.

False. A catalyst does not change the position of equilibrium. It speeds up both the forward and reverse reactions equally, so equilibrium is reached more quickly but the concentrations at equilibrium are unchanged.

State Le Chatelier's Principle .

Le Chatelier's Principle states that when the conditions of a system at equilibrium are changed, the system automatically responds to oppose the change.

Increasing the temperature of an equilibrium mixture shifts the position of equilibrium in the ______ direction. Decreasing temperature shifts it in the ______ direction.

Increasing the temperature of an equilibrium mixture shifts the position of equilibrium in the endothermic direction. Decreasing temperature shifts it in the exothermic direction.

Why does increasing pressure shift the position of equilibrium toward the side with fewer moles of gas?

By Le Chatelier's Principle, the system opposes an increase in pressure by reducing the total number of gas molecules. It shifts toward the side of the equation with fewer moles of gas to counteract the increased pressure.

What is the Haber process?

An industrial process used to manufacture ammonia (NH 3 ) from nitrogen and hydrogen.

Balance the chemical equation for the Haber proces: N 2 (g) + ______ H 2 (g) ⇌ ______ NH 3 (g)

The balanced chemical equation is: N 2 (g) + 3 H 2 (g) ⇌ 2 NH 3 (g)

State the sources of nitrogen and hydrogen used as raw materials in the Haber Process.

Nitrogen is obtained from the air; hydrogen is obtained from methane (natural gas).

True or False? In the Haber Process, increasing the temperature increases both the rate of reaction and the equilibrium yield of ammonia.

False. Increasing temperature increases the rate of reaction but decreases the equilibrium yield of ammonia, as the forward reaction is exothermic. A compromise temperature of 450°C is used.

Explain why 200 atm is used in the Haber Process rather than a much higher pressure.

Higher pressure increases yield, as the forward reaction produces fewer moles of gas. However, very high pressures are costly to maintain and create safety hazards, so 200 atm is used as a compromise.

The catalyst used in the Haber Process is ______ , which speeds up the rate at which equilibrium is reached but does not change the ______ of equilibrium.

The catalyst used in the Haber Process is iron , which speeds up the rate at which equilibrium is reached but does not change the position of equilibrium.

Give one use of ammonia produced by the Haber Process.

Ammonia is used to manufacture ammonium salts and nitrates, which are applied as NPK fertilisers to provide nitrogen for improved plant growth.

What is the Contact process?

An industrial process used to manufacture sulfuric acid (H 2 SO 4 ) from sulfur dioxide and oxygen.

State the sources of sulfur dioxide and oxygen used in the Contact process.

Sulfur dioxide is produced by burning sulfur or by roasting sulfide ores; oxygen is obtained from the air.

Balance the chemical equation for the Contact process: 2SO 2 (g) + O 2 (g) ⇌ ______ SO 3 (g)

The balanced chemical equation for the Contact process is: 2SO 2 (g) + O 2 (g) ⇌ 2 SO 3 (g)

True or False? In the Contact Process, increasing the temperature would increase the yield of SO 3 .

False. The forward reaction is exothermic, so increasing temperature shifts the equilibrium to the left, decreasing the yield of SO 3 . A temperature of 450°C is a compromise between rate of reaction and equilibrium yield.

Explain why a pressure of only about 2 atm is used in the Contact Process rather than a much higher pressure.

The equilibrium yield of SO 3 is already about 96% at 2 atm, so there is little economic benefit to increasing pressure. Very high pressures would also be costly and create safety hazards.

The catalyst used in the Contact Process is ______ . Removing the catalyst would decrease the rate of reaction but would not change the ______ of equilibrium.

The catalyst used in the Contact Process is vanadium(V) oxide (V 2 O 5 ) . Removing the catalyst would decrease the rate of reaction but would not change the position of equilibrium.

Give one use of sulfuric acid produced by the Contact Process.

Sulfuric acid is used in the manufacture of fertilisers. It is also used in car batteries, and in the production of soaps and detergents.

O LevelChemistryCambridge (CIE)Flashcards6. Chemical Reactions6.3 Reversible Reactions & Equilibrium

6.3 Reversible Reactions & Equilibrium (Cambridge (CIE) O Level Chemistry): Flashcards

Exam code: 5070

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What is a reversible reaction?

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Cards in this collection (29)

What is a reversible reaction?
A reversible reaction is one that can proceed in both directions. Products from the forward reaction can react to reform the original reactants in the reverse reaction. The symbol ⇌ is used in the equation.
True or False?
When water is added to white anhydrous copper(II) sulfate, the colour change observed is irreversible.
False.
The reaction is reversible. Anhydrous copper(II) sulfate absorbs water and turns blue. Heating the blue hydrated form drives off the water and restores the white anhydrous solid.
Anhydrous cobalt(II) chloride is ______. When water is added, it turns ______. This change can be reversed by ______.
Anhydrous cobalt(II) chloride is blue. When water is added, it turns pink. This change can be reversed by heating.
Why can cobalt(II) chloride and copper(II) sulfate be used as chemical tests for water?
Both undergo a visible colour change when they absorb water. Cobalt(II) chloride turns from blue to pink; copper(II) sulfate turns from white to blue. These distinct colour changes confirm the presence of water.
In the reaction CuSO₄ + 5H₂O ⇌ CuSO₄.5H₂O, the white anhydrous copper(II) sulfate turns ______ when it absorbs ______ of crystallisation.
In the reaction CuSO₄ + 5H₂O ⇌ CuSO₄.5H₂O, the white anhydrous copper(II) sulfate turns blue when it absorbs water of crystallisation.
What is water of crystallisation?
Water of crystallisation is water that is chemically included in the structure of a hydrated salt. It is represented by a dot in the formula, for example CuSO₄.5H₂O or CoCl₂.6H₂O.
What is the difference between a hydrated and an anhydrous salt?
A hydrated salt contains water of crystallisation chemically incorporated into its crystal structure. An anhydrous salt has had this water removed, usually by heating. The two forms are interconverted by a reversible reaction.
True or False?
When explaining how increased concentration of a reactant affects an equilibrium system, it is correct to use collision theory.
False.
For CIE O Level, equilibrium shift questions are answered using Le Chatelier's Principle — the system shifts in the direction that opposes the change. Simply stating that more collisions occur in one direction is not an accepted explanation.
What is dynamic equilibrium?
Dynamic equilibrium is the state reached in a reversible reaction when the rate of the forward reaction equals the rate of the reverse reaction. The concentrations of reactants and products remain constant, but both reactions continue to occur.
What happens to the position of equilibrium if the concentration of a reactant is increased?
The position of equilibrium shifts to the right. By Le Chatelier's Principle, the system opposes the increase by converting more reactant into product until a new equilibrium is established.
Equilibrium can only be established in a ______ system, where no reactants or products can ______.
Equilibrium can only be established in a closed system, where no reactants or products can escape.
True or False?
Adding a catalyst to an equilibrium mixture shifts the position of equilibrium to the right, increasing the yield of products.
False.
A catalyst does not change the position of equilibrium. It speeds up both the forward and reverse reactions equally, so equilibrium is reached more quickly but the concentrations at equilibrium are unchanged.
State Le Chatelier's Principle.
Le Chatelier's Principle states that when the conditions of a system at equilibrium are changed, the system automatically responds to oppose the change.
Increasing the temperature of an equilibrium mixture shifts the position of equilibrium in the ______ direction. Decreasing temperature shifts it in the ______ direction.
Increasing the temperature of an equilibrium mixture shifts the position of equilibrium in the endothermic direction. Decreasing temperature shifts it in the exothermic direction.
Why does increasing pressure shift the position of equilibrium toward the side with fewer moles of gas?
By Le Chatelier's Principle, the system opposes an increase in pressure by reducing the total number of gas molecules. It shifts toward the side of the equation with fewer moles of gas to counteract the increased pressure.
What is the Haber process?
An industrial process used to manufacture ammonia (NH₃) from nitrogen and hydrogen.
Balance the chemical equation for the Haber proces:
N₂ (g) + ______ H₂ (g) ⇌ ______ NH₃ (g)
The balanced chemical equation is:
N₂ (g) + 3H₂ (g) ⇌ 2NH₃ (g)
State the sources of nitrogen and hydrogen used as raw materials in the Haber Process.
Nitrogen is obtained from the air; hydrogen is obtained from methane (natural gas).
True or False?
In the Haber Process, increasing the temperature increases both the rate of reaction and the equilibrium yield of ammonia.
False.
Increasing temperature increases the rate of reaction but decreases the equilibrium yield of ammonia, as the forward reaction is exothermic. A compromise temperature of 450°C is used.
Explain why 200 atm is used in the Haber Process rather than a much higher pressure.
Higher pressure increases yield, as the forward reaction produces fewer moles of gas. However, very high pressures are costly to maintain and create safety hazards, so 200 atm is used as a compromise.
The catalyst used in the Haber Process is ______, which speeds up the rate at which equilibrium is reached but does not change the ______ of equilibrium.
The catalyst used in the Haber Process is iron, which speeds up the rate at which equilibrium is reached but does not change the position of equilibrium.
Give one use of ammonia produced by the Haber Process.
Ammonia is used to manufacture ammonium salts and nitrates, which are applied as NPK fertilisers to provide nitrogen for improved plant growth.
What is the Contact process?
An industrial process used to manufacture sulfuric acid (H₂SO₄) from sulfur dioxide and oxygen.
State the sources of sulfur dioxide and oxygen used in the Contact process.
Sulfur dioxide is produced by burning sulfur or by roasting sulfide ores; oxygen is obtained from the air.
Balance the chemical equation for the Contact process:
2SO₂ (g) + O₂ (g) ⇌ ______ SO₃ (g)
The balanced chemical equation for the Contact process is:
2SO₂ (g) + O₂ (g) ⇌ 2SO₃ (g)
True or False?
In the Contact Process, increasing the temperature would increase the yield of SO₃.
False.
The forward reaction is exothermic, so increasing temperature shifts the equilibrium to the left, decreasing the yield of SO₃. A temperature of 450°C is a compromise between rate of reaction and equilibrium yield.
Explain why a pressure of only about 2 atm is used in the Contact Process rather than a much higher pressure.
The equilibrium yield of SO₃ is already about 96% at 2 atm, so there is little economic benefit to increasing pressure. Very high pressures would also be costly and create safety hazards.
The catalyst used in the Contact Process is ______. Removing the catalyst would decrease the rate of reaction but would not change the ______ of equilibrium.
The catalyst used in the Contact Process is vanadium(V) oxide (V₂O₅). Removing the catalyst would decrease the rate of reaction but would not change the position of equilibrium.
Give one use of sulfuric acid produced by the Contact Process.
Sulfuric acid is used in the manufacture of fertilisers. It is also used in car batteries, and in the production of soaps and detergents.

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