Define dynamic equilibrium .

Dynamic equilibrium is a state in a closed system where the rate of the forward reaction equals the rate of the reverse reaction, and the concentrations of reactants and products remain constant .

True or False? At dynamic equilibrium, the concentrations of reactants and products are equal.

False. At dynamic equilibrium, concentrations remain constant — but they are not necessarily equal. The ratio of products to reactants depends on the position of equilibrium.

What condition must be met for a gaseous equilibrium to be established?

The reaction must occur in a closed system , so that no reactants or products can escape. In an open system, gases are lost to the surroundings and equilibrium cannot be reached.

At dynamic equilibrium, the rate of the .......... reaction equals the rate of the .......... reaction, and concentrations remain .......... .

At dynamic equilibrium, the rate of the forward reaction equals the rate of the reverse reaction, and concentrations remain constant .

True or False? At dynamic equilibrium, the forward and reverse reactions have both stopped.

False. At dynamic equilibrium both reactions are still occurring. The forward and reverse rates are equal, which is why concentrations stay constant — not because the reactions have stopped.

Why can a solution-phase equilibrium be reached in an open flask, but a gas-phase equilibrium cannot?

In solution, only a negligible amount of material is lost by evaporation, so the system behaves as effectively closed . For gaseous reactions, gases would escape to the surroundings in an open system, preventing equilibrium from being established.

A .......... system is one in which no reactants or products can escape. An .......... system allows matter and energy to be lost to the surroundings.

A closed system is one in which no reactants or products can escape. An open system allows matter and energy to be lost to the surroundings.

Define reversible reaction .

A reversible reaction is one in which the products can react to reform the original reactants. It is represented using two opposing half arrows: ⇌

Can dynamic equilibrium be reached whether you start with reactants or products?

Yes. The same equilibrium position is reached regardless of whether you start with reactants, products, or a mixture. Once equilibrium is established, concentrations of all species remain constant .

Define Le Chatelier's principle .

Le Chatelier's principle states that if a change is made to a system in dynamic equilibrium, the position of equilibrium shifts to oppose that change.

How does increasing the concentration of a reactant affect the position of equilibrium?

Increasing the concentration of a reactant shifts the equilibrium to the right , towards the products, to oppose the change by consuming the added reactant.

True or False? Adding more product to an equilibrium mixture shifts the position of equilibrium to the left.

True. Adding more product increases its concentration. The equilibrium shifts to the left to oppose this change, converting product back into reactants.

When the pressure is increased on an equilibrium mixture containing gases, the equilibrium shifts towards the side with .......... moles of gas.

When the pressure is increased on an equilibrium mixture containing gases, the equilibrium shifts towards the side with fewer moles of gas.

What effect does increasing temperature have on an exothermic equilibrium reaction?

Increasing temperature shifts the equilibrium to the left , favouring the endothermic (reverse) reaction. This reduces the yield of products for an exothermic forward reaction.

What effect does diluting an aqueous equilibrium mixture with water have on the position of equilibrium?

True. If the number of gas moles is equal on both sides of the equation, a change in pressure gives neither side an advantage and the position of equilibrium does not shift .

For an endothermic reaction, increasing temperature shifts the equilibrium to the .......... , increasing the yield of .......... .

For an endothermic reaction, increasing temperature shifts the equilibrium to the right , increasing the yield of products .

What effect does a catalyst have on the position of equilibrium?

Adding water decreases the concentration of all dissolved species. The equilibrium shifts to the side with more dissolved particles to partially restore concentrations (Le Chatelier's principle). If there are equal numbers of dissolved particles on each side, the equilibrium position is unaffected.

True or False? For an endothermic reaction, increasing temperature shifts the equilibrium to the right.

True. The system absorbs the added heat by favouring the endothermic (forward) reaction, shifting the position of equilibrium to the right and increasing the yield of products.

What is meant by a rate-yield compromise in an industrial process?

A rate-yield compromise is the selection of reaction conditions that balance the need for an acceptable rate of reaction with an acceptable yield of product, since the conditions that maximise one often reduce the other.

Why is a temperature of around 450 °C used in the Haber Process despite this giving a lower equilibrium yield?

The Haber Process is exothermic in the forward direction, so higher temperatures shift equilibrium left and reduce yield. Lower temperatures increase yield but slow the rate too much. Around 450 °C gives an acceptable yield (~35%) at an acceptable rate, balancing economics and efficiency.

In the Haber Process, the forward reaction is .......... , so increasing temperature .......... the yield of ammonia.

In the Haber Process, the forward reaction is exothermic , so increasing temperature decreases the yield of ammonia.

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

False. Increasing temperature increases the rate of reaction, but decreases the yield of ammonia because the forward reaction is exothermic. The equilibrium shifts left at higher temperatures.

Why does increasing pressure increase the yield of ammonia in the Haber Process?

The equation N 2 (g) + 3H 2 (g) ⇌ 2NH 3 (g) has 4 moles of gas on the left and 2 on the right. Increasing pressure shifts equilibrium to the side with fewer gas moles, favouring ammonia production.

In the Haber Process, a pressure of around .......... MPa is used as a compromise between yield and the .......... and .......... costs of generating very high pressures.

In the Haber Process, a pressure of around 20 MPa is used as a compromise between yield and the financial and energy costs of generating very high pressures.

True or False? Increasing pressure always increases the yield of a gaseous equilibrium reaction.

False. Increasing pressure shifts equilibrium towards the side with fewer moles of gas. If both sides have equal moles of gas, pressure has no effect on yield. The direction of shift depends on the stoichiometry of the equation.

What three categories of consideration must industry balance when selecting reaction conditions?

Industry must balance financial considerations (cost of conditions vs profit from increased yield), energy and environmental considerations (fossil fuel use and energy demands), and health and safety considerations (safe working conditions for high pressure or temperature).

What is a homogeneous system in the context of equilibrium?

A homogeneous system is one in which all reactants and products are in the same physical state . All species are included in the K c expression.

For the reaction aA + bB ⇌ cC + dD, the K c expression is written with the .......... concentrations raised to their stoichiometric powers in the .......... , divided by the .......... concentrations raised to their stoichiometric powers.

For the reaction aA + bB ⇌ cC + dD, the K c expression is written with the product concentrations raised to their stoichiometric powers in the numerator , divided by the reactant concentrations raised to their stoichiometric powers.

Write the K c expression for: N 2 (g) + 3H 2 (g) ⇌ 2NH 3 (g)

The K c expression is: K c = [NH 3 ] 2 / ([N 2 ][H 2 ] 3 ) Product concentrations appear in the numerator and reactant concentrations in the denominator, each raised to their stoichiometric coefficient .

True or False? Solids are included in the K c expression for a heterogeneous equilibrium.

False. Solids are excluded from K c expressions. Only aqueous and gaseous species are included. For example, in CaCO 3 (s) ⇌ CaO (s) + CO 2 (g), K c = [CO 2 ] only.

What is a heterogeneous system in the context of equilibrium?

A heterogeneous system is one in which the reactants and products are not all in the same physical state. Solids are excluded from the K c expression; only aqueous and gaseous species are included.

Write the K c expression for: Ag + (aq) + Fe 2+ (aq) ⇌ Ag (s) + Fe 3+ (aq)

The K c expression is: K c = [Fe 3+ ] / ([Ag + ][Fe 2+ ]) Ag (s) is a solid and is excluded from the expression. Only aqueous species are included.

Square brackets in a K c expression represent the .......... of a species in units of .......... .

Square brackets in a K c expression represent the concentration of a species in units of mol dm -3 .

True or False? The value of K c changes when temperature is changed but not when concentration is changed.

True. K c is specific to a given temperature . Changing concentration shifts the position of equilibrium but does not alter the value of K c . Only a change in temperature changes K c .

What does the magnitude of K c tell you about the position of equilibrium?

If K c > 1, the equilibrium lies to the right (products favoured). If K c < 1, the equilibrium lies to the left (reactants favoured). If K c = 1, the equilibrium lies roughly halfway between reactants and products.

A LevelChemistryEdexcelFlashcards1. Physical ChemistryEquilibrium I

Equilibrium I (Edexcel A Level Chemistry): Flashcards

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FrontDynamic Equilibrium
Define dynamic equilibrium.

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Cards in this collection (35)

Define dynamic equilibrium.
Dynamic equilibrium is a state in a closed system where the rate of the forward reaction equals the rate of the reverse reaction, and the concentrations of reactants and products remain constant.
True or False?
At dynamic equilibrium, the concentrations of reactants and products are equal.
False.
At dynamic equilibrium, concentrations remain constant — but they are not necessarily equal. The ratio of products to reactants depends on the position of equilibrium.
What condition must be met for a gaseous equilibrium to be established?
The reaction must occur in a closed system, so that no reactants or products can escape. In an open system, gases are lost to the surroundings and equilibrium cannot be reached.
At dynamic equilibrium, the rate of the .......... reaction equals the rate of the .......... reaction, and concentrations remain .......... .
At dynamic equilibrium, the rate of the forward reaction equals the rate of the reverse reaction, and concentrations remain constant.
True or False?
At dynamic equilibrium, the forward and reverse reactions have both stopped.
False.
At dynamic equilibrium both reactions are still occurring. The forward and reverse rates are equal, which is why concentrations stay constant — not because the reactions have stopped.
Why can a solution-phase equilibrium be reached in an open flask, but a gas-phase equilibrium cannot?
In solution, only a negligible amount of material is lost by evaporation, so the system behaves as effectively closed. For gaseous reactions, gases would escape to the surroundings in an open system, preventing equilibrium from being established.
A .......... system is one in which no reactants or products can escape. An .......... system allows matter and energy to be lost to the surroundings.
A closed system is one in which no reactants or products can escape. An open system allows matter and energy to be lost to the surroundings.
Define reversible reaction.
A reversible reaction is one in which the products can react to reform the original reactants. It is represented using two opposing half arrows: ⇌
Can dynamic equilibrium be reached whether you start with reactants or products?
Yes. The same equilibrium position is reached regardless of whether you start with reactants, products, or a mixture. Once equilibrium is established, concentrations of all species remain constant.
Define Le Chatelier's principle.
Le Chatelier's principle states that if a change is made to a system in dynamic equilibrium, the position of equilibrium shifts to oppose that change.
How does increasing the concentration of a reactant affect the position of equilibrium?
Increasing the concentration of a reactant shifts the equilibrium to the right, towards the products, to oppose the change by consuming the added reactant.
True or False?
Adding more product to an equilibrium mixture shifts the position of equilibrium to the left.
True.
Adding more product increases its concentration. The equilibrium shifts to the left to oppose this change, converting product back into reactants.
When the pressure is increased on an equilibrium mixture containing gases, the equilibrium shifts towards the side with .......... moles of gas.
When the pressure is increased on an equilibrium mixture containing gases, the equilibrium shifts towards the side with fewer moles of gas.
What effect does increasing temperature have on an exothermic equilibrium reaction?
Increasing temperature shifts the equilibrium to the left, favouring the endothermic (reverse) reaction. This reduces the yield of products for an exothermic forward reaction.
What effect does diluting an aqueous equilibrium mixture with water have on the position of equilibrium?
True.
If the number of gas moles is equal on both sides of the equation, a change in pressure gives neither side an advantage and the position of equilibrium does not shift.
For an endothermic reaction, increasing temperature shifts the equilibrium to the .........., increasing the yield of .......... .
For an endothermic reaction, increasing temperature shifts the equilibrium to the right, increasing the yield of products.
What effect does a catalyst have on the position of equilibrium?
Adding water decreases the concentration of all dissolved species. The equilibrium shifts to the side with more dissolved particles to partially restore concentrations (Le Chatelier's principle).
If there are equal numbers of dissolved particles on each side, the equilibrium position is unaffected.
True or False?
For an endothermic reaction, increasing temperature shifts the equilibrium to the right.
True.
The system absorbs the added heat by favouring the endothermic (forward) reaction, shifting the position of equilibrium to the right and increasing the yield of products.
What is meant by a rate-yield compromise in an industrial process?
A rate-yield compromise is the selection of reaction conditions that balance the need for an acceptable rate of reaction with an acceptable yield of product, since the conditions that maximise one often reduce the other.
Why is a temperature of around 450 °C used in the Haber Process despite this giving a lower equilibrium yield?
The Haber Process is exothermic in the forward direction, so higher temperatures shift equilibrium left and reduce yield. Lower temperatures increase yield but slow the rate too much. Around 450 °C gives an acceptable yield (~35%) at an acceptable rate, balancing economics and efficiency.
In the Haber Process, the forward reaction is .........., so increasing temperature .......... the yield of ammonia.
In the Haber Process, the forward reaction is exothermic, so increasing temperature decreases the yield of ammonia.
True or False?
In the Haber Process, increasing temperature increases both the rate of reaction and the yield of ammonia.
False.
Increasing temperature increases the rate of reaction, but decreases the yield of ammonia because the forward reaction is exothermic. The equilibrium shifts left at higher temperatures.
Why does increasing pressure increase the yield of ammonia in the Haber Process?
The equation N₂ (g) + 3H₂ (g) ⇌ 2NH₃ (g) has 4 moles of gas on the left and 2 on the right. Increasing pressure shifts equilibrium to the side with fewer gas moles, favouring ammonia production.
In the Haber Process, a pressure of around .......... MPa is used as a compromise between yield and the .......... and .......... costs of generating very high pressures.
In the Haber Process, a pressure of around 20 MPa is used as a compromise between yield and the financial and energy costs of generating very high pressures.
True or False?
Increasing pressure always increases the yield of a gaseous equilibrium reaction.
False.
Increasing pressure shifts equilibrium towards the side with fewer moles of gas. If both sides have equal moles of gas, pressure has no effect on yield. The direction of shift depends on the stoichiometry of the equation.
What three categories of consideration must industry balance when selecting reaction conditions?
Industry must balance financial considerations (cost of conditions vs profit from increased yield), energy and environmental considerations (fossil fuel use and energy demands), and health and safety considerations (safe working conditions for high pressure or temperature).
What is a homogeneous system in the context of equilibrium?
A homogeneous system is one in which all reactants and products are in the same physical state. All species are included in the K_c expression.
For the reaction aA + bB ⇌ cC + dD, the K_c expression is written with the .......... concentrations raised to their stoichiometric powers in the .........., divided by the .......... concentrations raised to their stoichiometric powers.
For the reaction aA + bB ⇌ cC + dD, the K_c expression is written with the product concentrations raised to their stoichiometric powers in the numerator, divided by the reactant concentrations raised to their stoichiometric powers.
Write the K_c expression for: N₂ (g) + 3H₂ (g) ⇌ 2NH₃ (g)
The K_c expression is: K_c = [NH₃]² / ([N₂][H₂]³)
Product concentrations appear in the numerator and reactant concentrations in the denominator, each raised to their stoichiometric coefficient.
True or False?
Solids are included in the K_c expression for a heterogeneous equilibrium.
False.
Solids are excluded from K_c expressions. Only aqueous and gaseous species are included. For example, in CaCO₃ (s) ⇌ CaO (s) + CO₂ (g), K_c = [CO₂] only.
What is a heterogeneous system in the context of equilibrium?
A heterogeneous system is one in which the reactants and products are not all in the same physical state. Solids are excluded from the K_c expression; only aqueous and gaseous species are included.
Write the K_c expression for: Ag⁺ (aq) + Fe²⁺ (aq) ⇌ Ag (s) + Fe³⁺ (aq)
The K_c expression is: K_c = [Fe³⁺] / ([Ag⁺][Fe²⁺])
Ag (s) is a solid and is excluded from the expression. Only aqueous species are included.
Square brackets in a K_c expression represent the .......... of a species in units of .......... .
Square brackets in a K_c expression represent the concentration of a species in units of mol dm^-3.
True or False?
The value of K_c changes when temperature is changed but not when concentration is changed.
True.
K_c is specific to a given temperature. Changing concentration shifts the position of equilibrium but does not alter the value of K_c. Only a change in temperature changes K_c.
What does the magnitude of K_c tell you about the position of equilibrium?
If K_c > 1, the equilibrium lies to the right (products favoured). If K_c < 1, the equilibrium lies to the left (reactants favoured). If K_c = 1, the equilibrium lies roughly halfway between reactants and products.

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