5.2 Equilibrium (Quantitative) for A-Level Chemistry (OCR)

What equilibrium constant is used for gaseous equilibria based on partial pressures?

Kp is used when all species are gases and pressures are used instead of concentrations.

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What quantity is used in the expression for Kp instead of concentration?

Partial pressure

Each gaseous species is represented by its partial pressure.

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Fill in the blank:

Kp can only be used for equilibria occurring entirely in the _______ phase.

gas

Kp applies to homogeneous gas-phase equilibria.

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True or False:

The value of Kp changes if the pressure of the system changes.

False

Changing pressure shifts equilibrium position but does not change Kp at constant temperature.

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At what condition does the value of Kp remain constant?

Constant temperature

Equilibrium constants only change when temperature changes.

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True or False:

Adding a catalyst changes the value of Kp.

False

Catalysts only speed up the attainment of equilibrium.

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Fill in the blank:

The pressure exerted by one gas in a mixture is called its _______ pressure.

partial

It represents the contribution of that gas to the total pressure.

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How can the partial pressure of a gas be calculated from mole fraction and total pressure?

Mole fraction × total pressure

Partial pressure = mole fraction × total pressure.

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True or False:

The powers in a Kp expression correspond to the stoichiometric coefficients in the balanced equation.

True

The same rule used in Kc expressions also applies to Kp.

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For the reaction aA + bB ⇌ cC + dD (all gases), how are products represented in the Kp expression?

Numerator

Kp = (P_C)^c(P_D)^d / (P_A)^a(P_B)^b.

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Fill in the blank:

A large value of Kp indicates equilibrium lies mainly towards the _______.

products

Most reactants are converted into products at equilibrium.

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What factor can change the value of Kp for a reaction?

Temperature

Changing temperature alters the equilibrium constant and equilibrium position.

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In a reversible reaction at equilibrium, how do the rates of the forward and reverse reactions compare?

Equal

Dynamic equilibrium means both reactions continue but occur at the same rate.

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What happens to the concentrations of reactants and products once equilibrium has been reached?

Remains constant

Concentrations stay constant because both reactions occur at equal rates, not because reactions stop.

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What principle predicts how a system at equilibrium responds to changes in temperature, pressure, or concentration?

Le Chatelier’s principle

It states that a system at equilibrium will oppose a change imposed on it.

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Fill in the blank:

If the concentration of a reactant is increased, the equilibrium shifts to _______ the added reactant.

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oppose

The system adjusts to reduce the effect of the change by favouring the reaction that consumes the added substance.

True or False:

At equilibrium, the forward and reverse reactions have stopped occurring.

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False

Equilibrium is dynamic: both reactions continue but at equal rates.

For a gaseous equilibrium, increasing pressure favours the side with _______ moles of gas.

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fewer

The system reduces pressure by shifting toward the side with fewer gas particles.

True or False:

Adding a catalyst changes the position of equilibrium in a reversible reaction.

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False

A catalyst speeds up both forward and reverse reactions equally but does not change equilibrium composition.

Why is a compromise temperature often used in industrial equilibrium reactions?

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Balance

A compromise balances reaction rate (faster at high temperature) and equilibrium yield (often better at lower temperature).

True or False:

Increasing temperature shifts equilibrium in the endothermic direction.

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True

Heat can be treated as a reactant in endothermic reactions, so increasing temperature favours that direction.

Fill in the blank:

If a product is removed from an equilibrium mixture, the equilibrium shifts to produce _______ product.

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Removing product reduces its concentration, so the system forms more to restore equilibrium.

True or False:

In a homogeneous equilibrium, all reactants and products are in the same physical state.

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True

Homogeneous equilibria typically involve all gases or all species dissolved in solution.

Why are high pressures sometimes avoided in industrial equilibrium processes even if they increase yield?

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Cost

High pressures require stronger equipment and more energy, increasing economic cost.

For a reversible reaction, how is the **equilibrium constant** expressed using the **concentrations of species**?

Products over reactants ## Footnote Each concentration is raised to the power of its stoichiometric coefficient in the balanced equation.

# Fill in the blank: The **concentration of a species** used in an **equilibrium expression** is written using _\_\_\_\_\_\_ brackets.

square ## Footnote For example, the concentration of A is written as [A].

What unit is typically used for **concentrations** in an **equilibrium expression for Kc**?

mol dm^-3 ## Footnote All concentrations used in Kc expressions are measured in mol dm^-3.

# True or False: The **value of Kc** changes if the **concentration of reactants or products** is altered.

False ## Footnote Changing concentration shifts the position of equilibrium but does not change the value of Kc.

For the reaction aA + bB ⇌ cC + dD, how are the **concentrations of products** used in the **Kc expression**?

Numerator ## Footnote The expression is Kc = [C]^c[D]^d / [A]^a[B]^b.

# True or False: Adding a **catalyst** changes the **value of Kc** for a reaction.

False ## Footnote A catalyst speeds up the attainment of equilibrium but does not alter the equilibrium constant.

At what **condition** must remain constant when calculating or comparing **values of Kc**?

Temperature ## Footnote The equilibrium constant only remains constant at a fixed temperature.

# Fill in the blank: If the **value of Kc** is very large, the **equilibrium mixture** contains mostly _\_\_\_\_\_\_.

products ## Footnote A large Kc indicates the equilibrium position lies far to the right.

# True or False: If **Kc** is very small, the **equilibrium position** lies towards the reactants.

True ## Footnote A small Kc means only a small amount of product is formed at equilibrium.

In a **homogeneous equilibrium**, in what **physical state** are all species present?

Same state ## Footnote Typically all gases or all substances dissolved in the same solution.

What must be known in order to **calculate the value of Kc** from **experimental data**?

Equilibrium concentrations ## Footnote Concentrations must be measured once the system has reached equilibrium.

# Fill in the blank: When calculating **Kc**, each **concentration** is raised to the power of its _\_\_\_\_\_\_ in the balanced equation.

coefficient ## Footnote The stoichiometric coefficient determines the exponent in the Kc expression.

5.2 Equilibrium (Quantitative) Flashcards

Calculate equilibrium constants and predict system behavior using Kc and Kp. (36 cards)