Chemical Equilibrium and Keq Quiz

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Questions and Answers

What does a large magnitude of Kc indicate about the concentrations of products and reactants?

  • Products are favored over reactants. (correct)
  • Reactants are favored over products.
  • The reaction is at equilibrium with no net change.
  • Products and reactants are present in equal concentrations.

In the equilibrium constant expression for the reaction CaCO3(s) ⇌ CaO(s) + CO2(g), which species is included in the expression?

  • Both CaCO3 and CaO.
  • Neither CaCO3 nor CaO.
  • Only CO2. (correct)
  • Only CaCO3.

How is the equilibrium constant for an overall reaction derived from multiple equilibria?

  • It is the product of the equilibrium constants of the individual reactions. (correct)
  • It is the difference of the equilibrium constants of the individual reactions.
  • It is the average of the equilibrium constants of the individual reactions.
  • It is the sum of the equilibrium constants of the individual reactions.

In a heterogeneous equilibrium, which of the following phases are involved?

<p>Different phases, such as solids, liquids, and gases. (D)</p> Signup and view all the answers

What does the equilibrium constant Kp represent in relation to Kc?

<p>It is only applicable to gaseous reactions. (D)</p> Signup and view all the answers

What characterizes a chemical equilibrium?

<p>The rates of the forward and reverse reactions are equal. (A)</p> Signup and view all the answers

What does the equilibrium constant (Keq) indicate when it is much greater than 1?

<p>The equilibrium lies to the right and favors the products. (D)</p> Signup and view all the answers

In the equilibrium constant expression $K_{eq} = \frac{[C]^c[D]^d}{[A]^a[B]^b}$, what do the symbols [A], [B], [C], and [D] represent?

<p>Molar concentrations of the chemical species. (A)</p> Signup and view all the answers

What happens to the reaction quotient (Qc) if the concentrations of reactants are increased before equilibrium is reached?

<p>Qc may either increase or decrease depending on the reaction. (B)</p> Signup and view all the answers

What does it mean if Keq is much smaller than 1?

<p>The equilibrium lies to the left and favors the reactants. (D)</p> Signup and view all the answers

Which of the following is true about the law of mass action?

<p>It establishes a constant ratio of reactant and product concentrations at equilibrium. (A)</p> Signup and view all the answers

When does the reaction quotient (Qc) become equal to the equilibrium constant (Kc)?

<p>When the system reaches equilibrium. (C)</p> Signup and view all the answers

What could cause a shift in the equilibrium position of a reaction?

<p>Changing the temperature of the system. (C)</p> Signup and view all the answers

What must happen to the reactants if $Q_c < K_c$?

<p>Reactants must be converted to products. (A)</p> Signup and view all the answers

Which statement is true if $K_c < 1$ for a reaction?

<p>There are more moles of reactants than products at equilibrium. (B)</p> Signup and view all the answers

What do $K_c$ and $K_p$ measure?

<p>Concentrations of aqueous solutions and gases. (B)</p> Signup and view all the answers

In the equilibrium reaction $2NO(g) + O_2(g) ⇌ 2NO_2(g)$, which concentration contributes to the calculation of $K_c$?

<p>All concentrations: [NO], [O_2], and [NO_2]. (A)</p> Signup and view all the answers

What is the role of $ riangle n$ in the relationship between $K_p$ and $K_c$?

<p>It indicates the change in moles of gas during the reaction. (B)</p> Signup and view all the answers

For the reaction $HF(aq) + H_2O(l) ⇌ H_3O^+(aq) + F^-(aq)$, what can be concluded about $K_p$?

<p>$K_p$ cannot be defined for this reaction. (B)</p> Signup and view all the answers

When does the reaction reach equilibrium in terms of $Q_c$ and $K_c$?

<p>All of the above. (D)</p> Signup and view all the answers

What does a larger value of $K_c$ indicate about a reaction?

<p>The products are favored over the reactants. (C)</p> Signup and view all the answers

Flashcards

Chemical Equilibrium

A state where the rates of forward and reverse reactions are equal, and the concentrations of reactants and products remain constant over time.

Equilibrium Constant (Keq)

A constant value representing the ratio of product concentrations to reactant concentrations at equilibrium.

Law of Mass Action

For a reversible reaction at equilibrium and a constant temperature, a specific ratio of reactant and product concentrations has a constant value (Keq).

Reaction Quotient (Qc)

A value calculated using the concentrations of reactants and products at that point in time during the reaction

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Equilibrium Constant Magnitude

The value of Keq indicates whether the equilibrium favors products or reactants.

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Comparing Qc and Kc

Comparing the reaction quotient (Qc) and the equilibrium constant (Kc) determines the direction a reaction will proceed to reach equilibrium.

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Dynamic Process

At equilibrium, both forward and reverse reactions continue, however there is no net change in the overall concentrations of reactants and products.

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Equilibrium Constant Expression

[𝐶]^𝑐[𝐷]^𝑑 / [𝐴]^𝑎[𝐵]^𝑏

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Large Kc value

A large equilibrium constant (Kc) indicates that the products are highly favored at equilibrium, meaning the concentration of products is significantly higher than the reactants.

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Heterogeneous Equilibria

A type of equilibrium involving reactants and products in different phases (solid, liquid, gas).

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Kp and Kc for solids

When dealing with solids in an equilibrium, their concentrations are considered constant and are combined into the equilibrium constant.

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Multiple Equilibria

A situation where the products of one equilibrium reaction act as reactants in another equilibrium reaction.

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Overall K for multiple equilibria

The overall equilibrium constant for a series of reactions is simply the product of the equilibrium constants for the individual reactions.

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Kc

The equilibrium constant expressed in terms of molar concentrations.

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Kp

The equilibrium constant expressed in terms of partial pressures.

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Q < K

The reaction will favor the formation of products to reach equilibrium.

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Q > K

The reaction will favor the formation of reactants to reach equilibrium.

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Q = K

The system is at equilibrium, the rates of forward and reverse reactions are equal, and the concentrations of reactants and products are not changing.

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Homogenous Equilibrium

An equilibrium where all reactants and products are in the same phase.

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Study Notes

Chemical Equilibrium

  • Chemical equilibrium occurs when the rates of forward and reverse reactions are equal, and the concentrations of reactants and products remain constant over time.
  • Both forward and reverse reactions still occur at equilibrium, but there's no net change in concentration.
  • Chemical equilibrium is dynamic.

Equilibrium Constant (Keq)

  • The equilibrium constant (Keq) expression is based on the concentrations of products and reactants at equilibrium.
  • Keq = [C]c[D]d / [A]a[B]b
  • [A], [B], [C], and [D] are the molar concentrations of the chemical species.
  • a, b, c, and d are the stoichiometric coefficients for the reacting species A, B, C, and D.
  • The magnitude of Keq indicates whether the equilibrium favors products or reactants.
  • If Keq >> 1, the equilibrium will favor products.
  • If Keq << 1, the equilibrium will favor reactants.

Reaction Quotient (Qc)

  • The reaction quotient (Qc) is used to determine the direction a reaction will proceed to reach equilibrium when the reaction is not at equilibrium.
  • Qc = [products]coefficients / [reactants]coefficients
  • Comparing Qc with Keq:
    • If Qc < Keq, the reaction will proceed in the forward direction (reactants to products).
    • If Qc = Keq, the reaction is at equilibrium.
    • If Qc > Keq, the reaction will proceed in the reverse direction (products to reactants).

Types of Equilibrium

  • Homogeneous Equilibria: All reactants and products are in the same phase (e.g., all gases).
  • Heterogeneous Equilibria: Reactants and products are in different phases (e.g., solid, liquid, gas). Concentrations of solids and pure liquids are NOT included in the equilibrium expression.

Factors Affecting Equilibrium

  • Concentration: Increasing the concentration of products shifts the equilibrium to the left, and decreasing the concentration of products shifts the equilibrium to the right.
  • Volume and Pressure (for gases): Increasing pressure (decreasing volume) favors the side with fewer moles of gas. Decreasing pressure (increasing volume) favors the side with more moles of gas. Changes in pressure do not affect the concentrations of solids or liquids.
  • Temperature: Increasing temperature favors endothermic reactions (absorbs heat). Decreasing temperature favors exothermic reactions (releases heat).
  • Catalyst: A catalyst speeds up the rate of both the forward and reverse reactions, but it does not affect the position of equilibrium.

Acid-Base Equilibria

  • Arrhenius Acid: Produces H+ ions in aqueous solutions.
  • Arrhenius Base: Produces OH¯ ions in aqueous solutions.
  • Bronsted-Lowry Acid: Proton (H+) donor.
  • Bronsted-Lowry Base: Proton (H+) acceptor.
  • Lewis Acid: Electron pair acceptor.
  • Lewis Base: Electron pair donor.
  • Strong Acids/Bases: Completely ionize in solution.
  • Weak Acids/Bases: Partially ionize in solution.

Ionization of Water and pH

  • Water undergoes self-ionization: H₂O + H₂O ↔ H₃O⁺ + OH⁻
  • Ion product constant (Kw) = [H₃O⁺][OH⁻] = 1.0 × 10⁻¹⁴ at 25°C
  • pH = -log[H₃O⁺] = -log[H⁺].

Solubility Equilibria

  • Solubility: The amount of solute that dissolves in a given amount of solvent at a specific temperature to form a saturated solution.
  • Molar Solubility: The number of moles of solute that dissolve in 1 liter of a saturated solution.
  • Solubility Equilibrium: Exists in a saturated solution when the rate of dissolution equals the rate of precipitation.
  • Solubility Product Constant (Ksp): The equilibrium constant for the dissolution of a sparingly soluble salt.

Metal-Complex Equilibria

  • Complex Ion: An ion with a central metal cation bonded to one or more ligands (molecules or ions).
  • Formation Constant (Kf): Equilibrium constant for the formation of a complex ion. Large Kf values indicate more stable complex ions.

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