MED-102 General Chemistry: Chemical Equilibrium 1
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Questions and Answers

What is the correct expression for the equilibrium constant Kc for the reaction CaCO3(s) ⇌ CaO(s) + CO2(g)?

  • Kc = [CaCO3]/[CaO][CO2]
  • Kc = [CaO][CO2]/[CaCO3] (correct)
  • Kc = [CaO][CO2]
  • Kc = [CaCO3]

Which statement correctly describes the relationship between Kp and Kc?

  • Kp = Kc (RT) for all reactions.
  • Kp and Kc are equal only at standard conditions. (correct)
  • Kp is always greater than Kc.
  • Kc = Kp when the reaction involves only pure solids.

How is a heterogeneous equilibrium different from a homogeneous equilibrium?

  • Heterogeneous equilibrium includes only gases.
  • Heterogeneous equilibrium only involves liquids.
  • Heterogeneous equilibrium includes both solids and gases. (correct)
  • Heterogeneous equilibrium has constant concentrations.

In the reaction 2 H2(g) + O2(g) ⇌ 2 H2O(g), if Kc = 2.4 × 10^47 at 500°C, what does this Kc value indicate about the equilibrium position?

<p>Equilibrium lies to the right. (B)</p> Signup and view all the answers

Which of the following is NOT considered when calculating the equilibrium constant Kc?

<p>Pure solids (A)</p> Signup and view all the answers

What happens to the direction of a reaction when Qc < Kc?

<p>The reaction will move to the right. (B)</p> Signup and view all the answers

Which components are included in the equilibrium constant Kc expression?

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

What is the Kc value for the reaction at 700 K given the expression H2(g) + I2(g) ⇌ 2 HI(g)?

<p>57.0 (B)</p> Signup and view all the answers

What occurs at dynamic equilibrium in a chemical reaction?

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

How is Kp related to Kc mathematically?

<p>Kp can be derived from Kc using the ideal gas law. (B)</p> Signup and view all the answers

What does it mean if Qc > Kc for a given reaction?

<p>The reaction will move to the left. (A)</p> Signup and view all the answers

Which of the following correctly describes homogeneous equilibria?

<p>Contain reactants and products in the same phase. (B)</p> Signup and view all the answers

What defines the state of dynamic equilibrium in a chemical reaction?

<p>Both forward and reverse reactions occur at equal rates. (B)</p> Signup and view all the answers

Which condition is essential for establishing dynamic equilibrium?

<p>There must be both forward and reverse reactions. (D)</p> Signup and view all the answers

Which of the following correctly describes how to write an equilibrium expression for the reaction A + B ⇌ C + D?

<p>K = [C][D]/[A][B] (A)</p> Signup and view all the answers

How is the equilibrium constant Kc related to Kp for a gas-phase reaction?

<p>Kp is related to Kc by the equation Kp = Kc (RT) ^ Δn. (D)</p> Signup and view all the answers

If a system at equilibrium is disturbed by changing the concentration of reactants, what will happen?

<p>The equilibrium will shift to the right to produce more products. (B)</p> Signup and view all the answers

In a heterogeneous equilibrium, which of the following statements is true?

<p>Only gaseous and aqueous substances appear in the equilibrium expression. (C)</p> Signup and view all the answers

What will occur if the temperature of an exothermic reaction at equilibrium is increased?

<p>The equilibrium will shift to the right, favoring reactants. (A)</p> Signup and view all the answers

For a reaction involving gases, if Kp = 0.01 at a certain temperature, what does this indicate about the reaction?

<p>The concentration of reactants is greater than that of products. (C)</p> Signup and view all the answers

Which of the following is an example of a system likely to reach dynamic equilibrium?

<p>A beaker of water evaporating into the air. (A)</p> Signup and view all the answers

Flashcards

Reaction Quotient (Qc)

A ratio of product concentrations to reactant concentrations, calculated using initial concentrations, to compare to the equilibrium constant.

Equilibrium Constant (Kc)

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

Qc < Kc

Reaction will shift to the right (products) to reach equilibrium condition.

Qc > Kc

Reaction will shift to the left (reactants) to reach equilibrium.

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Qc = Kc

Reaction is at equilibrium; there is no net change in concentration.

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Dynamic Equilibrium

Forward and reverse reaction rates are equal, resulting in no net change in concentrations of reactants and products.

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Equilibrium Mixture

The composition of the reaction mixture at equilibrium

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Kp vs Kc

Kp is the equilibrium constant expressed in terms of partial pressures of gases, while Kc is the equilibrium constant expressed in terms of molar concentrations. Kp and Kc are related by the equation: Kp = Kc(RT)^Δn, where Δn is the change in the number of moles of gas in the balanced reaction.

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Heterogeneous Equilibrium

A chemical equilibrium where reactants and products exist in different phases (e.g., solid, liquid, gas).

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Solid and Liquid Concentrations

In heterogeneous equilibria, pure solids and liquids are considered to have constant concentrations and are not included in the equilibrium expression. This is because their densities and molar masses are constant.

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Equilibrium Constant Value

The value of the equilibrium constant (Kc) indicates whether the equilibrium lies to the right (products) or to the left (reactants). A large Kc value means the equilibrium lies to the right, favoring product formation.

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Equilibrium Heavily to the Right

A large equilibrium constant (Kc) indicates the equilibrium lies heavily to the right, favoring product formation.

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What does chemical equilibrium answer?

It explains how far a reaction proceeds towards completion and the amount of product formed.

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What does NOT change in chemical equilibrium?

The concentrations of reactants and products remain constant over time.

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What is a reversible reaction?

A chemical reaction that can proceed in both forward and reverse directions.

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What is the equilibrium mixture?

The specific combination of reactants and products present at equilibrium.

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What is dynamic equilibrium?

A state where the rates of the forward and reverse reactions are equal, resulting in no net change in concentrations.

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What is required for dynamic equilibrium?

The process must be reversible, and the system must be closed (no escape of matter).

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How does the water analogy explain dynamic equilibrium?

When water enters and exits a tank at equal rates, the water level remains constant.

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What is the reason many reactions don't go to completion?

The reverse reaction competes with the forward reaction.

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Can equilibrium be reached from either direction?

Yes, starting with either reactants or products will lead to the same equilibrium mixture at a given temperature.

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Explain the color change in the N2O4/NO2 example.

At 273 K, the equilibrium favors N2O4 (colorless), resulting in a colorless container. At higher temperatures, the equilibrium shifts towards NO2 (brown), making the container appear brown. This is due to the endothermic nature of the reaction.

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Study Notes

Course Information

  • Course: MED-102 General Chemistry
  • Topic: Chemical Equilibrium 1

Learning Objectives (LOBs)

  • Describe dynamic equilibrium
  • Write equilibrium expressions
  • Calculate K from Kp and vice versa
  • Predict the direction of a chemical system to establish equilibrium

What is Chemical Equilibrium?

  • Chemical kinetics focuses on reaction speed ("how fast?")
  • Chemical equilibrium focuses on the extent of a reaction ("how far?")
  • Equilibrium is the state where reactant and product concentrations remain constant
  • The resulting mixture is called the "equilibrium mixture"
  • Equilibrium applies only to reversible reactions

Dynamic Equilibrium

  • Forward and reverse reactions continue
  • Rates of forward and reverse reactions are equal
  • No net change in reactant or product amounts

The Equilibrium State

  • Many reactions don't proceed to completion due to reverse reactions
  • Equilibrium can be reached from either reactant or product side
  • At a given temperature, the same equilibrium mixture will be reached

The Equilibrium Constant Kc

  • Kc is the equilibrium constant based on concentrations
  • Its formula: Kc = [C]c[D]d / [A]a[B]b
  • Subscript 'c' refers to concentrations (molarities)

Equilibrium Constant Kp

  • Kp is the equilibrium constant based on partial pressures
  • Its formula: Kp = (PC)c(PD)d / (PA)a(PB)b
  • For gaseous systems

Relating Kc to Kp

  • Kp = Kc(RT)Δn
  • Δn = moles of gaseous products - moles of gaseous reactants
  • Equilibrium constants (Kc and Kp) are unitless

Heterogeneous Equilibria

  • Reactants and products are in different phases
  • Pure solids and liquids do not appear in the equilibrium expression

Using the Equilibrium Expression

  • Calculate reaction quotients (Q)
  • Compare Q to K to predict reaction shift
  • Q < K: reaction shifts right to reach equilibrium
  • Q > K: reaction shifts left to reach equilibrium
  • Q = K: reaction is at equilibrium

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Chemical Equilibria 1 PDF

Description

This quiz covers key concepts of chemical equilibrium, including dynamic equilibrium and equilibrium expressions. Students will learn to calculate equilibrium constants and predict the direction of reactions. Test your understanding of reversible reactions and the equilibrium state.

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