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Easy Kc Chemistry: Calculate Equilibrium Constants!

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Aysha Akmal

24/01/2023

Chemistry

Edexcel A Level Chemistry - Topic 11 Further Equilibrium

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Physical chemistry

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Chemical equilibria, le chateliers principle and kc

Easy Kc Chemistry: Calculate Equilibrium Constants!

A comprehensive guide to equilibrium constant calculations and related concepts in chemistry, focusing on Kc and Kp calculations, heterogeneous equilibria, and the effects of changing conditions.

  • Equilibrium law fundamentals cover both homogeneous and heterogeneous reactions
  • How to calculate Kc in chemistry involves understanding concentration-based equilibrium expressions
  • Kp calculations specifically deal with gaseous equilibria using partial pressures
  • Effects of temperature on equilibrium constants are crucial for understanding system behavior
  • Practical applications include ICE tables and experimental determination methods
  • Changes in concentration and pressure affect equilibrium position but not the constant value at constant temperature
...

24/01/2023

515

equilibrium law states that, aA + bB cC + dD EQUILIBRIUIM RECAP *NOTE System must be at constant temperature homogeneous reactions equilibri

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Calculating Kc and Heterogeneous Equilibria

This section delves deeper into the process of calculating Kc and introduces the concept of heterogeneous equilibria.

To calculate Kc:

  1. Write the balanced equation
  2. Determine initial amounts of reactants and products
  3. Identify given equilibrium amounts
  4. Calculate other equilibrium amounts using stoichiometry
  5. Substitute values into the Kc expression

Example: For the reaction 2NOClgg ⇌ 2NOgg + Cl₂gg Given: 1.00 mol NOCl in 0.50 dm³ flask, 0.33 mol NO at equilibrium Kc = NONO² Cl2Cl₂ / NOClNOCl² = 0.0800 mol dm⁻³

Heterogeneous equilibria involve substances in different phases. In these systems, solids and pure liquids are not included in the Kc expression as their concentrations remain effectively constant.

Highlight: For heterogeneous equilibria, only include gases and aqueous species in the Kc expression.

Example: For CaCO₃ss ⇌ CaOss + CO₂gg, Kc = CO2CO₂

This simplification is due to the constant density of solids and pure liquids, which makes their concentrations invariant in the equilibrium expression.

equilibrium law states that, aA + bB cC + dD EQUILIBRIUIM RECAP *NOTE System must be at constant temperature homogeneous reactions equilibri

View

Gaseous Equilibria and Kp

This section introduces the concept of Kp, which is used for gaseous equilibria where partial pressures are more easily measured than concentrations.

Kp is expressed using partial pressures of gases instead of concentrations:

For aAgg + bBgg ⇌ cCgg + dDgg, Kp = PCc×PDdP_C^c × P_D^d / PAa×PBbP_A^a × P_B^b

Where P_A, P_B, P_C, and P_D are the partial pressures of gases A, B, C, and D respectively.

Vocabulary: Mole fraction - The proportion of a particular gas in a mixture, calculated as molesofgasmoles of gas / totalmolesofallgasestotal moles of all gases.

Vocabulary: Partial pressure - The pressure exerted by a single gas in a mixture, calculated as molefractionmole fraction × totalpressuretotal pressure.

To calculate Kp:

  1. Determine mole fractions of gases
  2. Calculate partial pressures
  3. Substitute values into the Kp expression

Example: For N₂gg + 3H₂gg ⇌ 2NH₃gg Given: 2.15 mol N₂, 6.75 mol H₂, 1.41 mol NH₃, total pressure 10.0 atm Calculate mole fractions, then partial pressures, and finally Kp

Understanding Kp is crucial for analyzing gaseous equilibria and complements the use of Kc for solution-based systems.

equilibrium law states that, aA + bB cC + dD EQUILIBRIUIM RECAP *NOTE System must be at constant temperature homogeneous reactions equilibri

View

Effects of Temperature on Equilibrium Constants

This section would typically discuss how temperature changes affect equilibrium constants and the position of equilibrium. However, the provided transcript does not contain specific information on this topic.

Highlight: The effects of temperature on equilibrium constants are an important aspect of chemical equilibria, but are not covered in the given material.

In general, temperature changes can shift the equilibrium position and alter the value of the equilibrium constant. This relationship is described by Le Chatelier's Principle and the van 't Hoff equation.

equilibrium law states that, aA + bB cC + dD EQUILIBRIUIM RECAP *NOTE System must be at constant temperature homogeneous reactions equilibri

View

Practice Problems and Applications

This section would usually provide additional practice problems and real-world applications of equilibrium constant calculations. However, the given transcript does not include such content.

Applying equilibrium concepts to practical situations helps reinforce understanding and demonstrates the relevance of these calculations in various fields of chemistry and chemical engineering.

Highlight: Practice problems are essential for mastering equilibrium constant calculations and understanding how to apply these concepts in different scenarios.

Students are encouraged to seek additional resources for practice problems related to Kc and Kp calculations, as well as explore how these concepts are used in industrial processes and environmental chemistry.

equilibrium law states that, aA + bB cC + dD EQUILIBRIUIM RECAP *NOTE System must be at constant temperature homogeneous reactions equilibri

View

Page 5: Effects of Changing Conditions

This page examines how various factors affect equilibrium constants and positions.

Definition: Le Chatelier's Principle explains how systems respond to changes in conditions.

Example: 2CrO₄²⁻aqaq + 2H⁺aqaq ⇌ Cr₂O₇²⁻aqaq + H₂Oll demonstrates how concentration changes affect equilibrium.

Highlight: Changing concentration does not alter Kc value as long as temperature remains constant.

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Subjects

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Physical chemistry

Chemical equilibria, le chateliers principle and kc

 

Chemistry

•

515

•

24 Jan 2023

•

6 pages

Easy Kc Chemistry: Calculate Equilibrium Constants!

user profile picture

Aysha Akmal

@ayshakmal

A comprehensive guide to equilibrium constant calculations and related concepts in chemistry, focusing on Kc and Kp calculations, heterogeneous equilibria, and the effects of changing conditions.

  • Equilibrium law fundamentals cover both homogeneous and heterogeneous reactions
  • How to calculate Kc in... Show more

equilibrium law states that, aA + bB cC + dD EQUILIBRIUIM RECAP *NOTE System must be at constant temperature homogeneous reactions equilibri

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Calculating Kc and Heterogeneous Equilibria

This section delves deeper into the process of calculating Kc and introduces the concept of heterogeneous equilibria.

To calculate Kc:

  1. Write the balanced equation
  2. Determine initial amounts of reactants and products
  3. Identify given equilibrium amounts
  4. Calculate other equilibrium amounts using stoichiometry
  5. Substitute values into the Kc expression

Example: For the reaction 2NOClgg ⇌ 2NOgg + Cl₂gg Given: 1.00 mol NOCl in 0.50 dm³ flask, 0.33 mol NO at equilibrium Kc = NONO² Cl2Cl₂ / NOClNOCl² = 0.0800 mol dm⁻³

Heterogeneous equilibria involve substances in different phases. In these systems, solids and pure liquids are not included in the Kc expression as their concentrations remain effectively constant.

Highlight: For heterogeneous equilibria, only include gases and aqueous species in the Kc expression.

Example: For CaCO₃ss ⇌ CaOss + CO₂gg, Kc = CO2CO₂

This simplification is due to the constant density of solids and pure liquids, which makes their concentrations invariant in the equilibrium expression.

equilibrium law states that, aA + bB cC + dD EQUILIBRIUIM RECAP *NOTE System must be at constant temperature homogeneous reactions equilibri

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Gaseous Equilibria and Kp

This section introduces the concept of Kp, which is used for gaseous equilibria where partial pressures are more easily measured than concentrations.

Kp is expressed using partial pressures of gases instead of concentrations:

For aAgg + bBgg ⇌ cCgg + dDgg, Kp = PCc×PDdP_C^c × P_D^d / PAa×PBbP_A^a × P_B^b

Where P_A, P_B, P_C, and P_D are the partial pressures of gases A, B, C, and D respectively.

Vocabulary: Mole fraction - The proportion of a particular gas in a mixture, calculated as molesofgasmoles of gas / totalmolesofallgasestotal moles of all gases.

Vocabulary: Partial pressure - The pressure exerted by a single gas in a mixture, calculated as molefractionmole fraction × totalpressuretotal pressure.

To calculate Kp:

  1. Determine mole fractions of gases
  2. Calculate partial pressures
  3. Substitute values into the Kp expression

Example: For N₂gg + 3H₂gg ⇌ 2NH₃gg Given: 2.15 mol N₂, 6.75 mol H₂, 1.41 mol NH₃, total pressure 10.0 atm Calculate mole fractions, then partial pressures, and finally Kp

Understanding Kp is crucial for analyzing gaseous equilibria and complements the use of Kc for solution-based systems.

equilibrium law states that, aA + bB cC + dD EQUILIBRIUIM RECAP *NOTE System must be at constant temperature homogeneous reactions equilibri

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Effects of Temperature on Equilibrium Constants

This section would typically discuss how temperature changes affect equilibrium constants and the position of equilibrium. However, the provided transcript does not contain specific information on this topic.

Highlight: The effects of temperature on equilibrium constants are an important aspect of chemical equilibria, but are not covered in the given material.

In general, temperature changes can shift the equilibrium position and alter the value of the equilibrium constant. This relationship is described by Le Chatelier's Principle and the van 't Hoff equation.

equilibrium law states that, aA + bB cC + dD EQUILIBRIUIM RECAP *NOTE System must be at constant temperature homogeneous reactions equilibri

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Practice Problems and Applications

This section would usually provide additional practice problems and real-world applications of equilibrium constant calculations. However, the given transcript does not include such content.

Applying equilibrium concepts to practical situations helps reinforce understanding and demonstrates the relevance of these calculations in various fields of chemistry and chemical engineering.

Highlight: Practice problems are essential for mastering equilibrium constant calculations and understanding how to apply these concepts in different scenarios.

Students are encouraged to seek additional resources for practice problems related to Kc and Kp calculations, as well as explore how these concepts are used in industrial processes and environmental chemistry.

equilibrium law states that, aA + bB cC + dD EQUILIBRIUIM RECAP *NOTE System must be at constant temperature homogeneous reactions equilibri

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Page 5: Effects of Changing Conditions

This page examines how various factors affect equilibrium constants and positions.

Definition: Le Chatelier's Principle explains how systems respond to changes in conditions.

Example: 2CrO₄²⁻aqaq + 2H⁺aqaq ⇌ Cr₂O₇²⁻aqaq + H₂Oll demonstrates how concentration changes affect equilibrium.

Highlight: Changing concentration does not alter Kc value as long as temperature remains constant.

equilibrium law states that, aA + bB cC + dD EQUILIBRIUIM RECAP *NOTE System must be at constant temperature homogeneous reactions equilibri

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Equilibrium Law and Constant (Kc)

The equilibrium law is a fundamental concept in chemistry that describes the state of a reversible reaction when the forward and reverse rates are equal. This section introduces the equilibrium constant Kc and its calculation.

For a general reaction aA + bB ⇌ cC + dD, the equilibrium constant Kc is expressed as:

Kc = CC^c DD^d / AA^a BB^b

Where AA, BB, CC, and DD represent the equilibrium concentrations of reactants and products.

Highlight: The equilibrium constant Kc is only valid for systems at constant temperature.

Example: For the reaction CH₃CO₂H aqaq + C₂H₅OH aqaq ⇌ CH₃CO₂C₂H₅ aqaq + H₂O ll, Kc = CH3CO2C2H5(aq)CH₃CO₂C₂H₅ (aq) H2O(l)H₂O (l) / CH3CO2H(aq)CH₃CO₂H (aq) C2H5OH(aq)C₂H₅OH (aq)

The units of Kc depend on the stoichiometry of the reaction. In some cases, Kc may be unitless.

Vocabulary: ICE table - A method for organizing Initial, Change, and Equilibrium concentrations in equilibrium calculations.

The value of Kc provides information about the position of equilibrium:

  • Large Kc: Products predominate at equilibrium
  • Kc ≈ 1: Significant amounts of both reactants and products present
  • Small Kc: Reactants predominate at equilibrium

Definition: Equilibrium position - The relative amounts of reactants and products present when a system reaches equilibrium.

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