Equilibrium in Chemistry and Physical Processes
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Questions and Answers

What is the pH calculation for salts of weak acid and strong base, for example CH3COONa?

  • pH = 7 + pK_a + log C
  • pH = 7 - pK_a - log C
  • pH = 7 - pK_a + log C
  • pH = 7 + pK_a - log C (correct)
  • Which type of buffer solution is designed to resist changes in pH when small amounts of acid or alkali are added?

  • Acidic buffer solution
  • Neutral buffer solution
  • Basic buffer solution
  • All of the above (correct)
  • In which category does a salt with solubility greater than 0.1M fall?

  • Insoluble
  • Slightly soluble
  • Moderately soluble
  • Soluble (correct)
  • What is the pH calculation for salts of strong acid and weak base, such as NH4Cl?

    <p>pH = 7 - pK_b - log C (D)</p> Signup and view all the answers

    What does a deviation in pH from the normal range in body fluids indicate?

    <p>Malfunctioning of the body (A)</p> Signup and view all the answers

    What ions are produced when NaCl is dissolved in an aqueous solution?

    <p>Na+ and Cl− (A)</p> Signup and view all the answers

    Which of the following is an example of a weak electrolyte?

    <p>CH3COOH (B)</p> Signup and view all the answers

    According to the Arrhenius theory, what do acids produce when dissolved in water?

    <p>Hydrogen ions (H+) (D)</p> Signup and view all the answers

    In the Brönsted-Lowry theory, what role does a base play?

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

    Which of the following compounds is classified as a strong electrolyte?

    <p>H2SO4 (A)</p> Signup and view all the answers

    What is the product of the ionization of sodium hydroxide (NaOH) in water?

    <p>Na+ and OH− (A)</p> Signup and view all the answers

    What characterizes a strong electrolyte?

    <p>Completely ionizes in solution (A)</p> Signup and view all the answers

    In the context of Lewis theory, which statement is true about acids?

    <p>Acids accept electron pairs (A)</p> Signup and view all the answers

    How does a positive $ΔH$ affect the equilibrium constant of an endothermic reaction as temperature changes?

    <p>The equilibrium constant increases with temperature increase. (B)</p> Signup and view all the answers

    What is the primary effect of changing pressure on a gaseous reaction when the number of moles of products differs?

    <p>It affects the yield of products based on the volume change. (B)</p> Signup and view all the answers

    When the volume of a system decreases, how does the equilibrium shift?

    <p>Towards the side with fewer moles of gas. (B)</p> Signup and view all the answers

    What role does a catalyst play in a chemical reaction?

    <p>It increases the rate of both forward and reverse reactions. (C)</p> Signup and view all the answers

    What occurs when an inert gas is added to a system at constant volume?

    <p>The equilibrium of the reaction remains unaffected. (B)</p> Signup and view all the answers

    Which of the following statements relates to ionic equilibrium in solution?

    <p>Only electrolytes can conduct electricity in the presence of ions. (B)</p> Signup and view all the answers

    According to Le-Chatlier’s principle, which factors can affect the equilibrium in a reaction?

    <p>Pressure, volume, and concentration changes. (D)</p> Signup and view all the answers

    In the reaction $Fe^{3+} (aq) + SCN^{-} (aq) \rightleftharpoons [Fe(SCN)]^{2+} (aq)$, what happens when the concentration of $SCN^{-}$ increases?

    <p>The equilibrium shifts to the right. (C)</p> Signup and view all the answers

    What does the term $K_a$ represent in acid-base chemistry?

    <p>Acid dissociation constant (C)</p> Signup and view all the answers

    How is the equilibrium concentration of the acid $HX$ expressed when ionization occurs?

    <p>$C - C\alpha$ (D)</p> Signup and view all the answers

    What is the correct expression for the base ionization constant $K_b$?

    <p>$\frac{[M^+] [OH^-]}{[MOH]}$ (C)</p> Signup and view all the answers

    Which equation represents the ionization of the weak base $MOH$?

    <p>$MOH \rightleftharpoons M^+ + OH^-$ (A)</p> Signup and view all the answers

    What relationship does $pK_a$ have with the acid dissociation constant $K_a$?

    <p>$pK_a = -\log(K_a)$ (D)</p> Signup and view all the answers

    How do salts behave in water during hydrolysis?

    <p>Salts may form hydrated ions or reform corresponding acids or bases (A)</p> Signup and view all the answers

    If $C$ is the initial concentration of a weak acid, what represents the concentration of the dissociated ion at equilibrium?

    <p>$C\alpha$ (D)</p> Signup and view all the answers

    Which statement is true about the equilibrium constant for weak acids and bases?

    <p>The ionization constant indicates the strength of the ion (C)</p> Signup and view all the answers

    What does the equilibrium constant indicate about a reaction?

    <p>It remains constant regardless of temperature changes. (B)</p> Signup and view all the answers

    What happens to the value of the equilibrium constant when the reaction is reversed?

    <p>It becomes the inverse of its original value. (A)</p> Signup and view all the answers

    How is the equilibrium constant affected when the equation is multiplied by 2?

    <p>It is squared. (B)</p> Signup and view all the answers

    If the equilibrium constant is greater than 1000, which of the following can be concluded?

    <p>The reaction favors the formation of products. (A)</p> Signup and view all the answers

    What does a reaction quotient Q indicate when Q is less than K?

    <p>The reaction proceeds in the direction of the products. (D)</p> Signup and view all the answers

    In a scenario where you know the initial concentrations but the equilibrium concentrations are unknown, what is the first step you must take?

    <p>Writing the balanced equation for the reaction. (A)</p> Signup and view all the answers

    Which of the following statements about catalysts in a reaction is correct?

    <p>They affect the time it takes to reach equilibrium. (D)</p> Signup and view all the answers

    What is the purpose of calculating the reaction quotient Q?

    <p>To predict the direction of the reaction. (A)</p> Signup and view all the answers

    What type of equilibrium is present when reactants and products have more than one phase?

    <p>Heterogeneous equilibrium (D)</p> Signup and view all the answers

    According to Le Chatelier's principle, what happens when the concentration of a reactant is increased?

    <p>The equilibrium shifts to the right to consume the added reactant. (C)</p> Signup and view all the answers

    What is the general effect of temperature increase on an exothermic reaction's equilibrium constant?

    <p>The equilibrium constant decreases. (C)</p> Signup and view all the answers

    What type of equilibrium exists between water vapor and liquid water?

    <p>Heterogeneous equilibrium (D)</p> Signup and view all the answers

    What consequence does a change in pressure have on equilibrium involving gases?

    <p>It will shift the equilibrium in the direction that reduces the number of gas molecules. (A)</p> Signup and view all the answers

    When a solid is in equilibrium with its saturated solution, what type of equilibrium is this considered?

    <p>Heterogeneous equilibrium (D)</p> Signup and view all the answers

    Which factor does NOT affect the equilibrium position of a reaction?

    <p>Change in the total volume of the environment (D)</p> Signup and view all the answers

    What happens to the equilibrium composition when a product is removed from a system at equilibrium?

    <p>The system shifts to produce more of that product. (B)</p> Signup and view all the answers

    Flashcards

    Homogeneous Equilibrium

    A reaction where all reactants and products are in the same physical state (gas, liquid, or solid)

    Heterogeneous Equilibrium

    A reaction where reactants and products exist in different physical states.

    Le Chatelier's Principle

    A principle stating that a system at equilibrium will shift to relieve stress caused by changes in conditions.

    Effect of Concentration Change on Equilibrium

    Adding a reactant or product to an equilibrium system will cause the reaction to shift in a direction that consumes the added substance.

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    Effect of Concentration Change on Equilibrium

    Removing a reactant or product from an equilibrium system will cause the reaction to shift in a direction that produces that substance.

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    Effect of Temperature Change on Equilibrium

    Increasing temperature favors the endothermic reaction; decreasing temperature favors the exothermic reaction.

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    Effect of Temperature Change on Equilibrium Constant

    The equilibrium constant (K) changes with temperature.

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    Reaction Quotient (Q)

    The reaction quotient (Q) measures the relative amounts of reactants and products at a given moment.

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    Equilibrium Constant (Kc)

    A constant that represents the ratio of products to reactants at equilibrium, where each concentration is raised to the power of its stoichiometric coefficient.

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    Equilibrium Constant - Independence

    The equilibrium constant is independent of the initial concentrations of reactants and products. It only depends on the temperature.

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    Favorable Equilibrium (Kc > 10^3)

    If the equilibrium constant (Kc) is greater than 10^3, the reaction strongly favors the formation of products at equilibrium.

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    Unfavorable Equilibrium (Kc < 10^-3)

    If the equilibrium constant (Kc) is less than 10^-3, the reaction strongly favors the formation of reactants at equilibrium.

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    Reaction Quotient and Equilibrium

    When Qc < Kc: the reaction proceeds forward, favoring the formation of products. When Qc > Kc: the reaction proceeds in the reverse direction, favoring the formation of reactants. When Qc = Kc: the reaction is at equilibrium.

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    Calculating Equilibrium Concentrations

    A series of steps involved in solving equilibrium problems where you know initial concentrations but not equilibrium concentrations. This involves writing the balanced equation, creating an ICE (Initial, Change, Equilibrium) table, and using Kc to solve for equilibrium concentrations.

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    Catalyst and Equilibrium Constant

    Adding a catalyst to a reaction does not change the equilibrium constant (Kc). It only speeds up the rate at which equilibrium is reached.

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    Electrolytes

    Substances that dissolve in water to produce ions, allowing them to conduct electricity.

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    Strong Electrolytes

    Electrolytes that dissociate completely into ions when dissolved in water.

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    Weak Electrolytes

    Electrolytes that only partially dissociate into ions when dissolved in water.

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    Bronsted-Lowry Theory

    A theory that defines acids as substances that donate hydrogen ions (H+) and bases as substances that accept hydrogen ions (H+).

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    Lewis Acid-Base Theory

    A theory that defines acids as substances that accept electron pairs and bases as substances that donate electron pairs.

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    Ionic Equilibrium

    A state of balance where the rate of the forward reaction equals the rate of the reverse reaction.

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    Equilibrium Expression

    A chemical equation that represents the equilibrium between ions and undissociated molecules in a weak electrolyte.

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    Effect of Pressure Change on Equilibrium

    The effect of pressure change on a reaction at equilibrium depends on the change in the total number of moles of gaseous products. If the number of moles of gaseous products increases, the equilibrium shifts to the left, and vice versa.

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    Pressure Change on Solids & Liquids

    Pressure changes don't significantly affect the equilibrium of reactions involving only solids or liquids because their volumes are relatively constant.

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    Effect of Volume Change on Equilibrium

    Decreasing the volume of a reaction vessel is equivalent to increasing the pressure, and vice versa. This shift in equilibrium favors the side with fewer moles of gas.

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    Effect of Catalyst on Equilibrium

    A catalyst speeds up a chemical reaction by providing an alternative pathway with lower activation energy, but it doesn't affect the equilibrium position. It speeds up both forward and reverse reactions equally.

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    Effect of Inert Gas Addition

    Adding an inert gas (like argon) to a reaction system at constant volume doesn't change the equilibrium position. This is because the partial pressures of the reactants and products remain constant.

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    Electrolytes vs. Non-electrolytes

    Electrolytes are substances that conduct electricity when dissolved in water because they dissociate into ions. Non-electrolytes don't conduct electricity because they don't produce ions in solution.

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    Buffer Solutions

    Solutions that resist changes in pH when diluted or when small amounts of acid or alkali are added.

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    Hydrolysis of Salts

    The pH of a salt solution depends on the strength of the acid and base that formed it.

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    Acidic Buffer

    A solution containing a weak acid and its conjugate base.

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    Basic Buffer

    A solution containing a weak base and its conjugate acid.

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    Solubility

    The ability of a substance to dissolve in a solvent.

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    Acid Dissociation Constant (Ka)

    The degree to which an acid ionizes in solution; a measure of acid strength. Higher Ka values indicate stronger acids.

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    Base Ionization Constant (Kb)

    The equilibrium constant for the ionization of a weak base; a measure of base strength. Higher Kb values indicate stronger bases.

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    pKa

    The negative logarithm of the acid dissociation constant (Ka). A lower pKa value indicates a stronger acid.

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    pKb

    The negative logarithm of the base ionization constant (Kb). A lower pKb value indicates a stronger base.

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    Degree of Ionization (α)

    The extent to which an acid or base ionizes in solution. A measure of the fraction of molecules that break down into ions.

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    Initial Concentration (C)

    The initial concentration of an undissociated acid or base before ionization occurs.

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    Expression of Ka and Kb using C and α

    A way to represent the equilibrium constant for the ionization of a weak acid or base using initial concentration and degree of ionization. It simplifies calculations for these systems.

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    Study Notes

    Equilibrium in Chemistry

    • Equilibrium is a dynamic process where the rates of forward and backward reactions are equal, resulting in no net change in the concentrations of reactants and products.
    • At equilibrium, the rate of evaporation equals the rate of condensation.
    • Equilibrium mixture is a mixture of reactants and products in their equilibrium state.

    Equilibrium in Physical Processes

    • Equilibrium in physical processes, such as phase transformations (solid-liquid, liquid-gas, solid-gas), can be better understood by observing characteristics at equilibrium.
    • Examples include solid-liquid equilibrium (ice and water at a specific temperature and pressure), and liquid-vapour equilibrium (liquid and its vapor).
    • Solid-liquid equilibrium: At a given temperature and pressure, both processes occur simultaneously and at the same rate. (Ice melting and water freezing.)
    • Liquid-vapour: The rate of evaporation and condensation are equal, maintaining a constant vapor pressure.
    • Important factors affecting phase transformations may include temperature and pressure.

    Equilibrium in Chemical Processes

    • Chemical equilibrium describes reversible reactions where the forward and reverse reaction rates are equal at a specific temperature.
    • Reversible reactions show a decrease in reactants and an increase in products over time.
    • Irreversible reactions proceed in one direction only until the reactants are consumed.
    • Equilibrium is a dynamic state where the forward and reverse reactions occur at the same rate, so the concentrations of reactants and products remain constant.
    • A state of equilibrium is characterized by a minimum Gibbs free energy.

    Equilibrium Constant

    • At a given temperature, a constant ratio exists between products and reactants at equilibrium.
    • Equilibrium constant (K) depends only on temperature, not initial concentrations. Larger K values favor products more than reactants.
    • For a reversible reaction aA + bB ⇌ cC + dD, the equilibrium constant is expressed as: K = [C]^c[D]^d / [A]^a[B]^b.

    Calculating Equilibrium Concentrations

    • In problems where initial concentrations are known but equilibrium concentrations are not, a three-step process is used include:
    • Writing a balanced equation
    • Setting up a table listing initial concentrations, changes, and equilibrium concentrations.
    • Substituting equilibrium concentrations into the equilibrium constant expression.

    Predicting the Direction of Reaction

    • The reaction quotient (Q) allows predicting if the reaction will shift toward products or reactants.
    • If Q < K: The ratio of products to reactants is less than that at equilibrium, so the reaction will shift forward (toward products).
    • If Q > K: The ratio of products to reactants is greater than that at equilibrium, so the reaction will shift backward (toward reactants).
    • If Q = K: The ratio of products to reactants is equal to that at equilibrium, and the reaction is at equilibrium.

    Effect of Changing Conditions on Equilibrium

    • Le Chatelier's principle describes how changes in conditions (concentration, temperature, pressure, catalyst) affect equilibrium—systems respond to counteract the change.
    • Concentration changes cause a shift to the side that consumes the added substance, or produces substance that's removed.
    • Temperature changes favor the exothermic process to counteract temperature changes, either increasing or decreasing temperature depending on the sign of enthalpy changes.
    • Pressure changes shift the equilibrium toward the side with fewer gas molecules to counteract the pressure change.

    Homogeneous and Heterogeneous Equilibria

    • Homogeneous equilibrium involves all reactants and products in the same phase.
    • Heterogeneous equilibrium involves reactants and products in different phases.

    Ionic Equilibria

    • Ionic equilibria involve the ionization of electrolytes (strong or weak) in solution, and these processes reach equilibrium.
    • Strong electrolytes completely dissociate, while weak electrolytes partially dissociate.

    Hydrolysis of Salts

    • Salt hydrolysis occurs when the ions from a salt react with water to produce an acidic or basic solution.
    • Strength of electrolyte is relevant in these reactions.

    Buffer Solutions

    • Solutions that resist changes in pH upon addition of small amounts of acid or base.
    • Mixtures of a weak acid or base and its conjugate base or acid create buffer solutions. Buffers maintain constant pH.

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    Description

    This quiz explores the concept of equilibrium in both chemical reactions and physical processes. It covers dynamic equilibrium, phase transformations, and examples such as solid-liquid and liquid-vapor equilibria. Test your understanding of how these equilibria operate and their implications in various scenarios.

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