Chemistry Equilibrium Concepts
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Questions and Answers

What happens to the reaction rate for the forward reaction when the volume decreases in a gaseous reaction?

  • It stops completely.
  • It remains constant.
  • It increases more than the reverse reaction. (correct)
  • It decreases significantly.

How does the addition of an inert gas affect the equilibrium position of a reaction?

  • It does not affect the equilibrium position. (correct)
  • It causes the reaction to cease.
  • It shifts the equilibrium to the right.
  • It shifts the equilibrium to the left.

What is the effect of increasing the total pressure in a reaction involving gases?

  • It increases the frequency of successful collisions for the products.
  • It decreases the total number of collisions.
  • It increases the rate of reaction for both forward and reverse reactions equally.
  • It increases the collision frequency among reactant particles. (correct)

Which of the following statements regarding catalysts is accurate?

<p>They speed up the rate of both forward and reverse reactions equally. (B)</p> Signup and view all the answers

Why does the reaction rate increase when there are more moles of reactants present?

<p>It leads to a greater frequency of collisions among reactant particles. (C)</p> Signup and view all the answers

What does a reaction with Q < K indicate about the direction of the reaction?

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

Which factor is solely responsible for changing the equilibrium constant K?

<p>Temperature changes (D)</p> Signup and view all the answers

In an endothermic reaction, how does an increase in temperature affect K?

<p>K increases. (B)</p> Signup and view all the answers

What does colorimetry analyze?

<p>The absorption of light at a specific wavelength. (C)</p> Signup and view all the answers

Which would cause a system to establish a new equilibrium?

<p>Changing the pressure or volume. (B)</p> Signup and view all the answers

What color does the iron(III) thiocyanate complex appear as?

<p>Blood-red (B)</p> Signup and view all the answers

If Q = K, what can we infer about the system?

<p>The system is at equilibrium. (D)</p> Signup and view all the answers

Which of the following reactions will decrease the value of K if the temperature is increased?

<p>An exothermic reaction. (A)</p> Signup and view all the answers

What type of reaction is photosynthesis considered to be?

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

What does a positive enthalpy change imply about a process?

<p>The process absorbs heat (A)</p> Signup and view all the answers

Which statement is true regarding the entropy change of photosynthesis?

<p>ΔS is less than zero (C)</p> Signup and view all the answers

What characterizes an irreversible chemical reaction based on ΔG?

<p>ΔG &gt; 0 for all temperatures (D)</p> Signup and view all the answers

What distinguishes photosynthesis from respiration regarding their reaction conditions?

<p>Photosynthesis and respiration occur under vastly different conditions (C)</p> Signup and view all the answers

Which type of reaction is characterized by ΔG < 0?

<p>Exergonic reaction (C)</p> Signup and view all the answers

What is true about competing drives in reversible reactions?

<p>They balance entropy and enthalpy effects (B)</p> Signup and view all the answers

Which reaction is an example of a spontaneous reaction with a negative ΔG?

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

What occurs during the dehydration of cobalt(II) chloride hexahydrate?

<p>It forms cobalt(II) chloride dihydrate and releases water. (D)</p> Signup and view all the answers

What is the primary characteristic of a reversible reaction?

<p>Its products can be converted back into reactants. (B)</p> Signup and view all the answers

Which of the following statements is true regarding the thermodynamic properties of forward and reverse reactions?

<p>If a forward reaction is exothermic, the reverse reaction is endothermic. (B)</p> Signup and view all the answers

What color does anhydrous cobalt(II) chloride appear as?

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

What happens when cobalt(II) chloride is dissolved in water?

<p>It produces a pink solution of cobalt(II) chloride hexahydrate. (D)</p> Signup and view all the answers

In the context of ionic compounds, what does solubility equilibria help to understand?

<p>It aids in predicting the formation of precipitates based on Ksp values. (C)</p> Signup and view all the answers

What is the outcome of mixing potassium chloride and silver nitrate solutions?

<p>Formation of a silver chloride precipitate. (D)</p> Signup and view all the answers

Which factor can significantly influence the solubility of ionic compounds in water?

<p>The temperature and pressure conditions. (B)</p> Signup and view all the answers

What is required to ensure that the equilibrium position lies heavily to the right in the creation of standard solutions of iron thiocyanate?

<p>The concentration of iron (III) nitrate must be at least 100 times greater. (D)</p> Signup and view all the answers

Which statement accurately describes the relationship between iron thiocyanate and thiocyanate ions during the reaction?

<p>The amount of thiocyanate consumed is virtually equal to the amount of iron thiocyanate produced. (C)</p> Signup and view all the answers

What is the recommended condition for creating standard solutions of iron thiocyanate using potassium thiocyanate?

<p>The concentration of SCN should be significantly greater than that of Fe. (A)</p> Signup and view all the answers

What principle underlies the solubility rule "like dissolves like"?

<p>Solutes dissolve if intermolecular forces between solute and solvent are more favorable. (D)</p> Signup and view all the answers

Which of the following is not relevant when discussing the equilibrium of a reversible reaction like the one used for creating iron thiocyanate?

<p>Limiting reagents. (D)</p> Signup and view all the answers

In the context of creating standard solutions of iron thiocyanate, what does the equilibrium constant Keq provide information about?

<p>The amount of product produced at equilibrium relative to the reactants. (B)</p> Signup and view all the answers

Which ion must be present in large excess when creating standard solutions of iron thiocyanate for effective colorimetry?

<p>Thiocyanate ions. (C)</p> Signup and view all the answers

What does the formation of intermolecular forces between solute and solvent signify when determining solubility?

<p>They must exceed forces between solvent molecules. (A)</p> Signup and view all the answers

What does the term 'positional disorder' refer to in thermodynamics?

<p>The energy configurations of a substance (C)</p> Signup and view all the answers

What is the mathematical expression for the change in entropy during a reaction?

<p>∆S_reaction = ΣS_products - ΣS_reactants (B)</p> Signup and view all the answers

Which statement about absolute entropy is true?

<p>Absolute entropy is theoretically zero for a perfect crystal lattice at 0K. (B)</p> Signup and view all the answers

According to the First Law of Thermodynamics, energy movement into or out of a system is governed by which principle?

<p>Conservation of energy (C)</p> Signup and view all the answers

The Second Law of Thermodynamics states that the entropy of which type of system will increase over time?

<p>An isolated system not at equilibrium (A)</p> Signup and view all the answers

What occurs in the process of combustion?

<p>A substance reacts with oxygen to produce energy (B)</p> Signup and view all the answers

What characterizes the Third Law of Thermodynamics?

<p>Entropy of a system approaches a minimum as temperature approaches zero (D)</p> Signup and view all the answers

The Zeroth Law of Thermodynamics states which of the following?

<p>If two systems are in thermal equilibrium with a third system, they are in thermal equilibrium with each other (C)</p> Signup and view all the answers

Flashcards

Reversible reaction

A chemical reaction that can proceed in both forward and reverse directions, where products can react to re-form reactants.

Thermodynamic properties of reverse reactions

The reverse reaction has opposite thermodynamic properties to the forward reaction. For example, if the forward reaction is exothermic, the reverse reaction is endothermic.

Cobalt(II) chloride hydration/dehydration

A reaction that changes the hydration state of cobalt(II) chloride, with different colours for each hydration state. Step 1: Cobalt(II) chloride hexahydrate (dark pink) loses water to form dihydrate (purple).

Anhydrous

The state of a substance that contains no water or other solvent molecules

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Cobalt(II) chloride dehydration process

Step 2: Cobalt(II) chloride dihydrate (purple) loses water to form anhydrous cobalt(II) chloride (sky blue).

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Cobalt(II) chloride Hydration process

The reverse reaction: Anhydrous cobalt(II) chloride (sky blue) reacts with water to form hexahydrate (dark pink).

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Hydration

The addition of water molecules to a substance.

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Dehydration

The removal of water molecules from a substance.

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Entropy

A measure of the disorder or randomness within a chemical system. The more disordered a system is, the higher its entropy. Units: J mol-1 K-1 or kJ mol-1 K-1

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Standard entropy (S°)

The standard entropy of a substance measures its disorder at 298K and 100 kPa. It represents the entropy change when a substance is heated from 0K to 298K.

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Entropy change (ΔS)

The change in entropy during a chemical reaction. Calculated by subtracting the sum of the reactants' entropies from the sum of the products' entropies.

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Entropy change of surroundings (ΔSsurroundings)

The entropy change of the surroundings during a reaction. It can be calculated using the enthalpy change and temperature of the reaction.

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Total entropy change (ΔSuniverse)

The total entropy change for a process is the sum of the entropy change of the system and the entropy change of the surroundings. The total entropy change of an isolated system is always positive.

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First Law of Thermodynamics

The first law of thermodynamics states that energy cannot be created or destroyed, only transferred or transformed. It is based on the principle of conservation of energy.

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Second Law of Thermodynamics

The second law of thermodynamics states that the entropy of an isolated system always increases over time. Systems tend to move toward a state of greater disorder or randomness.

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Third Law of Thermodynamics

The third law of thermodynamics states that the entropy of a perfect crystal at absolute zero (0K) is zero. This means that there is no disorder or randomness at absolute zero.

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Endothermic Reaction

A chemical reaction where energy is absorbed from the surroundings, resulting in a positive enthalpy change (∆𝐻 > 0).

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Exothermic Reaction

A chemical reaction that releases energy into the surroundings, causing a decrease in enthalpy (∆𝐻 < 0).

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Forward Entropy Drive

A reaction where the products are less ordered than the reactants, leading to an increase in entropy (∆𝑆 > 0).

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Reverse Entropy Drive

A reaction where the products are more ordered than the reactants, resulting in a decrease in entropy (∆𝑆 < 0).

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Exergonic Reaction

A reaction where the change in Gibbs Free Energy (∆𝐺) is negative, indicating that the reaction is spontaneous and releases free energy.

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Endergonic Reaction

A reaction where the change in Gibbs Free Energy (∆𝐺) is positive, indicating that the reaction is non-spontaneous and requires energy input.

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Reversibility in Chemical Reactions

In a reversible reaction, the forward reaction tends to have a positive enthalpy change (∆𝐻 > 0) and a positive entropy change (∆𝑆 > 0), while the reverse reaction has a negative enthalpy change (∆𝐻 < 0) and a negative entropy change (∆𝑆 < 0).

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Photosynthesis and Respiration

Photosynthesis and respiration are not a forward and reverse reaction pair because they occur under significantly different conditions.

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Effect of Inert Gas on Equilibrium

Adding an inert gas to a reaction mixture at constant volume increases the total pressure but does not affect the partial pressures of reactants or products. Since equilibrium depends on partial pressures, the equilibrium position remains unchanged.

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Effect of Inert Gas on Reaction Rate

While inert gas addition doesn't affect equilibrium position, it can slow down the reaction rate. This is because the inert gas molecules collide with reactant molecules, reducing the frequency of reactant-reactant collisions, which are needed for the reaction to occur.

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Le Chatelier's Principle and Inert Gas Addition

Le Chatelier's Principle states that if a change in conditions is applied to a system at equilibrium, the system will shift in a direction that relieves the stress. Adding an inert gas at constant volume increases total pressure, but doesn't change partial pressures, so no shift occurs.

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Volume Decrease and Equilibrium Shift

The forward reaction rate increases to a greater extent than the reverse reaction rate when volume decreases, since there are more collisions between reactants due to their higher concentration. This leads to a shift in equilibrium towards the product side.

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Pressure Increase & Equilibrium Shift

When volume decreases, the total pressure increases. This increase in pressure favors the side of the reaction with fewer gas molecules, as it reduces the stress on the system.

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Equilibrium constant (Keq)

The extent to which a reaction proceeds towards products at a given temperature. It is the ratio of products to reactants at equilibrium.

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Chemical equilibrium

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

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Dissolution of ionic compounds in water

The process of dissolving an ionic compound in water, where the ions are surrounded by water molecules and become separated.

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Solubility

The ability of a solute to dissolve in a solvent. It is influenced by the intermolecular forces between the solute and solvent.

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Saturated Solution

A solution where the solute concentration is equal to or greater than its solubility, leading to the formation of a precipitate.

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Unsaturated Solution

A solution where the solute concentration is less than its solubility.

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Supersaturated Solution

A solution where the solute concentration is greater than its solubility. It is unstable and the excess solute will precipitate out.

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Reaction Quotient (Q)

A measure of the relative amounts of reactants and products present at a given time in a reversible reaction. It indicates the direction the reaction will shift to reach equilibrium.

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Equilibrium

The state of a reversible reaction where the forward and reverse reaction rates are equal, resulting in no net change in the concentrations of reactants and products.

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Temperature and Equilibrium Constant

The change in the equilibrium constant (K) in response to changes in temperature. It depends on whether the reaction is exothermic or endothermic.

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Colorimetry

A method of analysis that uses the absorption of light at specific wavelengths to determine the concentration of a colored substance in solution.

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Le Chatelier's Principle

A principle stating that a system at equilibrium will shift to relieve stress. This shift may be towards products or reactants, depending on the stress applied.

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Iron Thiocyanate Reaction

The reaction between iron ions (Fe3+) and thiocyanate ions (SCN-) in solution to form a blood-red complex ion (FeSCN2+)

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Colorimetric Analysis

The process of measuring the concentration of a substance in solution by determining the amount of light it absorbs or transmits at a specific wavelength.

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Study Notes

IQ1 - Static and Dynamic Equilibrium

  • Chemical reactions don't always go to completion, some are reversible
  • Practical investigations analyze the reversibility of chemical reactions (e.g., cobalt(II) chloride, iron(III) nitrate, potassium thiocyanate, burning magnesium, burning steel wool)
  • Develop models to illustrate static and dynamic equilibrium, contrasting open and closed systems
  • Analyze non-equilibrium systems in terms of entropy and enthalpy changes (e.g., combustion, photosynthesis)
  • Explore the relationship between collision theory and reaction rate in relation to chemical equilibrium reactions (ACSCH070, ACSCH094)

IQ2 - Factors that Affect Equilibrium

  • Investigate how temperature, concentration, volume, and pressure affect equilibrium
  • Le Chatelier's principle predicts the effects of change in reaction conditions
  • Examples: heating cobalt(II) chloride hydrate, interaction between nitrogen dioxide and dinitrogen tetroxide, iron(III) thiocyanate
  • Explore how activation energy and heat of reaction influence the position of equilibrium

IQ3 - Calculating the Equilibrium Constant (Keq)

  • Deduce equilibrium expressions (Keq) for homogeneous reactions in solution.
  • Calculate Keq and concentrations of substances in equilibrium systems
  • Understand how temperature influences Keq
  • Conduct investigations to find Keq of a chemical reaction (e.g., iron(III) thiocyanate).
  • Investigate the use of Keq in various chemical reactions (e.g., dissociation of ionic solutions, acid/base dissociation)

IQ4 - Solution Equilibria

  • Analyze ionic compound solubility in water
  • Explore the role of intermolecular forces in dissolution
  • Investigate solubility rules to predict solubility outcomes
  • Learn how different ions affect the solubility of substances
  • Understand how solubility and chemical equilibrium are related

Modelling Dynamic Equilibrium

  • Advantages: -Demonstrates that the rate of forward reaction is proportional to reactants and the reverse reaction is proportional to products. -Models cases where the stoichiometric ratio isn't 1:1. -Show that equilibrium can be re-established if disturbed

  • Disadvantages:

  • Doesn't deal with concentration

  • Water loss can happen

  • Only works for one reactant/product

  • Doesn't show reactant to product transformation

Collision Theory

  • Successful collisions require sufficient energy and correct orientation for reaction.
  • Explains reversible reaction rates, where the rate of the forward reaction is initially high and decreases as reactants are used up; while the rate of the reverse reaction is initially low, and increase as products are formed.
  • Explains how a state of dynamic equilibrium where forward and reverse reaction rates are equal

Equilibrium Constant

  • Quantitative relation between reactant and product concentrations at equilibrium
  • The ratio of product concentrations to reactant concentrations, raised to the power of their stoichiometric coefficients in a balanced equation
  • Represents the extent of a reaction in a specific direction

Equilibrium, Temperature, and Catalysts

  • Temperature affects equilibrium by favoring exothermic or endothermic reactions depending on the temperature change
  • Catalysts change the rate of both forward and reverse reactions equally, so they don't change the equilibrium position.

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Description

Explore the principles of static and dynamic equilibrium in chemical reactions. This quiz covers factors that affect equilibrium, including temperature and concentration, along with practical investigations and models. Engage with concepts like Le Chatelier's principle and reaction rates to deepen your understanding of chemical systems.

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