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Interactive Audio Lesson
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Dynamic Equilibrium
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Today, we're going to discuss dynamic equilibrium, which is a state where the forward and reverse reactions occur at the same rate. Can anyone explain why we call it 'dynamic'?
Because even though the concentrations of the products and reactants remain constant, the reactions are still happening!
Exactly! This means that at equilibrium, there is no net change, but processes are actively continuing. Can someone think of an example of a system at equilibrium?
How about the evaporation of water? It evaporates and also condenses at the same rate when it reaches equilibrium!
Great example! To remember this concept, think of the phrase 'constant activity at balance.' Remember, dynamic means ongoing!
Le Chatelierβs Principle
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Now, letβs discuss Le Chatelierβs Principle. This principle says that if a system at equilibrium is subjected to a change, the system adjusts to counter that change. What kind of changes can affect equilibrium?
I think adding or removing reactants or products can change the equilibrium.
What about changing the temperature or pressure?
Exactly! Remember the acronym CTP: Concentration, Temperature, Pressure. If we increase the concentration of a reactant, for instance, the reaction will shift to produce more products. Can anyone provide a scenario where this applies?
In the Haber process, if we remove ammonia from the system, the equilibrium would shift to produce more ammonia.
Excellent! Always think about how equilibrium has a tendency to restore balance.
Equilibrium Constants
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Moving on to equilibrium constants, Kc and Kp are vital in understanding how favorable a reaction is at equilibrium. Why do you think these constants are valuable?
They help us predict the concentrations of products and reactants at equilibrium.
Correct! For any given reaction, Kc tells us the ratio of product concentrations to reactant concentrations at equilibrium. Can anyone write the expression for Kc for the reaction: 2NO(g) + O2(g) βΆ 2NO2(g)?
Kc = [NO2]^2 / ([NO]^2[O2]).
Perfect! And remember, when calculating Kc, always use the concentrations at equilibrium, and units are typically molarity.
Introduction & Overview
Read a summary of the section's main ideas. Choose from Basic, Medium, or Detailed.
Quick Overview
Standard
The exercises cover the concepts of dynamic equilibrium, including equilibrium constants, Le Chatelier's principle, and the impact of pressure, temperature, and concentration changes on equilibria. The exercises also relate to the understanding of acids and bases, along with the ionization of weak acids and bases.
Detailed
Exercises in Chemical Equilibria
This section focuses on a range of exercises that challenge the reader's understanding of chemical equilibria. The exercises include problems related to calculating equilibrium constants, understanding the implications of Le Chatelier's principle, and exploring the effects of concentration changes on equilibrium states. Key concepts include:
- Dynamic Equilibrium: The continuous process of chemical reactions reaching rates of formation that balance reactants and products.
- Equilibrium Constants: Understanding how to calculate and interpret the equilibrium constants for reactions.
- Le Chatelierβs Principle: Application of this principle to predict the shift in equilibria with changes in concentration, pressure, and temperature.
- Acid-Base Equilibria: Working with weak acids and bases, their ionization constants, and how concentrations affect the resulting pH of solutions.
- Solubility Products: Exercises that involve calculating the solubility of sparingly soluble salts and understanding the common ion effect on solubility.
The section aims to provide a comprehensive set of problems that cover theoretical knowledge and practical applications, fostering a deeper understanding of the principles governing chemical equilibria.
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Audio Book
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Effect of Volume Increase on Vapour Pressure
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A liquid is in equilibrium with its vapour in a sealed container at a fixed temperature. The volume of the container is suddenly increased.
a) What is the initial effect of the change on vapour pressure?
b) How do rates of evaporation and condensation change initially?
c) What happens when equilibrium is restored finally and what will be the final vapour pressure?
Detailed Explanation
When the volume of a container with a liquid in equilibrium with its vapour is suddenly increased, the initial effect is a decrease in vapour pressure. This occurs because there is now more space for the vapour, and thus the concentration of vapour molecules decreases immediately. As a result, the rate of condensation (the process by which vapour turns back to liquid) becomes greater than the rate of evaporation (the process by which liquid turns to vapour). However, over time, as the system adjusts back to equilibrium, the rates of condensation and evaporation will become equal again, restoring the equilibrium. The final vapour pressure will stabilize at a new value that is lower than before the volume change, depending on the temperature of the liquid.
Examples & Analogies
Think of a soda can. When you open the can (increase the volume available to the gas), the fizz (the pressure of carbon dioxide gas) decreases initially as the gas escapes into open air (the vapour pressure drops). Once you open it, the gas expands into the environment, changing the rates of bubbling and fizzing from the liquid until it levels out.
Calculating Kc from Equilibrium Concentrations
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What is Kc for the following equilibrium when the equilibrium concentration of each substance is: [SO2]= 0.60M, [O2] = 0.82M and [SO3] = 1.90M?
2SO2(g) + O2(g) 2SO3(g)
Detailed Explanation
To calculate Kc, we use the equilibrium constant expression, which for this reaction is defined as Kc = [SO3]^2 / ([SO2]^2 * [O2]). Plugging in the given concentrations:
- [SO3] = 1.90 M
- [SO2] = 0.60 M
- [O2] = 0.82 M.
Calculating:
Kc = (1.90)^2 / ((0.60)^2 * (0.82)) = 3.61 / (0.36 * 0.82) = 3.61 / 0.2952 β 12.24. Therefore, Kc for the reaction is approximately 12.24.
Examples & Analogies
Imagine a busy cafΓ©. The number of people sitting at tables (analogous to products) versus those working at the counter or coming in for takeout (analogous to reactants) can be thought of in terms of an equilibrium state. If more people start leaving the cafΓ©, the atmosphere becomes less busy (similar to an increase in product concentration), changing the overall dynamics until a new balance is reached with a fresh set of customers.
Calculating Kp from Equilibrium Mixture
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At a certain temperature and total pressure of 105Pa, iodine vapour contains 40% by volume of I atoms
I2 (g) 2I (g)
Calculate Kp for the equilibrium.
Detailed Explanation
To calculate Kp for the equilibrium involving iodine gas, we start by determining the partial pressures of the species involved. Given that 40% of the volume consists of I atoms, if we consider a total pressure of 105 Pa, the partial pressure of I2 can be calculated as 60% of the total since 60% corresponds to the undissociated I2. The partial pressure of I2 = 0.60 * 105 Pa = 63 Pa. The partial pressure of I is twice that of I2 because of the reaction stoichiometry. Thus, (2I) = 2*63 Pa = 126 Pa. Plugging these into the expression for Kp:
Kp = (P_I^2) / (P_I2) = (126)^2 / (63) = 252. Hence, Kp = 126 Pa.
Examples & Analogies
Consider a traffic system: more cars on the road (analogous to greater pressure from I) vs the road's capacity (stock of resources, analogous to I2). In a dense traffic jam, more drivers will attempt to move ultimately leading to stagnation, managing a new balance until a new equilibrium in traffic flow is established.
Equilibrium Constant Expressions
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Write the expression for the equilibrium constant, Kc for each of the following reactions:
(i) 2NOCl (g) 2NO (g) + Cl2 (g)
(ii) 2Cu(NO3)2 (s) 2CuO (s) + 4NO2 (g) + O2 (g)
(iii) CH3COOC2H5(aq) + H2O(l) CH3COOH (aq) + C2H5OH (aq)
(iv) Fe3+ (aq) + 3OHβ (aq) Fe(OH)3 (s)
(v) I2 (s) + 5F2 2IF5
Detailed Explanation
To write the equilibrium constant expressions (Kc) for each of these reactions, we need to consider only the species that are in the gaseous or aqueous phases, as solids and liquids do not appear in Kc expressions:
(i) Kc = [NO]^2 [Cl2] / [NOCl]^2
(ii) Kc = [NO2]^4 [O2] / [Cu(NO3)2]^2 (solids are not included)
(iii) Kc = [CH3COOH][C2H5OH] / [CH3COOC2H5]
(iv) Kc = [Fe3+][OHβ]^3 (the product here is a solid, which is excluded)
(v) Kc = [IF5]^2 / [I2][F2]^5.
Kc gives a way to express the relationship between the concentration of products to reactants at equilibrium, highlighting the importance of coefficients from the balanced equation.
Examples & Analogies
Think about a recipe where you have a certain number of ingredients. Only the ones that influence the final dish's taste and texture need to be considered β for instance, flour and sugar in cake batter (analogous to products) whilst ignoring the baking tray or kitchen counter (solids). In cooking, just like writing Kc, you focus on the essentials that determine the outcome β similar to what is included in the equilibrium expression.
Definitions & Key Concepts
Learn essential terms and foundational ideas that form the basis of the topic.
Key Concepts
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Dynamic equilibrium is when reactant and product concentrations remain constant but reactions are ongoing.
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Le Chatelier's principle explains how system equilibria shift in response to external changes.
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Equilibrium constants (Kc, Kp) describe the balance of products to reactants at equilibrium.
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Solubility products (Ksp) relate to the saturation concentrations of ionic compounds in solution.
Examples & Real-Life Applications
See how the concepts apply in real-world scenarios to understand their practical implications.
Examples
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For the reaction 2SO2(g) + O2(g) β 2SO3(g), if [SO2] = 0.60 M and [O2] = 0.82 M, the equilibrium constant Kc can be calculated and interpreted.
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In the dissolution of BaSO4(s) into Ba2+(aq) and SO42β(aq), the Ksp expression is given by Ksp = [Ba2+][SO42β].
Memory Aids
Use mnemonics, acronyms, or visual cues to help remember key information more easily.
π΅ Rhymes Time
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Equilibrium's balance can sway, concentration changes lead the way.
π Fascinating Stories
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Imagine a seesaw; when one side gets heavier, it shifts to restore balance. Thatβs how equilibrium works!
π§ Other Memory Gems
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Remember CTP (Concentration, Temperature, Pressure) when discussing Le Chatelierβs Principle.
π― Super Acronyms
Kc = Concentration for Products over Reactants.
Flash Cards
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Glossary of Terms
Review the Definitions for terms.
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Term: Dynamic Equilibrium
Definition:
A state in which the rates of the forward and reverse reactions are equal, resulting in constant concentrations of reactants and products.
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Term: Le Chatelier's Principle
Definition:
A principle stating that a change in the conditions of a system at equilibrium will cause the system to adjust to counteract that change.
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Term: Equilibrium Constant (Kc)
Definition:
A numerical value that describes the ratio of product concentrations to reactant concentrations at equilibrium.
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Term: Solubility Product Constant (Ksp)
Definition:
An equilibrium constant applied to the dissolution of sparingly soluble salts.
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Term: Ionization Constant (Ka/Kb)
Definition:
The equilibrium constant for the ionization of an acid or base in solution.