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Chemical equilibria, Le Chatelier's principle and Kc
This topic applies equilibrium ideas to reversible reactions and equilibrium constants.
10
Objectives
10
Flashcards
10
Questions
90 min
Study time
AqaA LevelChemistryPhysical chemistry
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Start revising Chemical equilibria, Le Chatelier's principle and Kc
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10 objective pages available
Equilibrium and Le Chatelier's principle5 objectives
- Define dynamic equilibrium in a closed system.
- Use Le Chatelier's principle to predict the effect of concentration changes.
- Use Le Chatelier's principle to predict the effect of pressure changes.
- Use Le Chatelier's principle to predict the effect of temperature changes.
- Explain why catalysts do not change the position of equilibrium.
Equilibrium constant Kc5 objectives
- Construct Kc expressions for homogeneous equilibria.
- Calculate Kc from equilibrium concentrations.
- Calculate equilibrium concentrations from Kc where appropriate.
- Determine units for Kc.
- Interpret the magnitude of Kc in terms of equilibrium position.
Key terms
Dynamic EquilibriumLe Chatelier's PrincipleEquilibriumConcentrationMole RatioExothermic ReactionCatalystEquilibrium constant (Kc)Homogeneous equilibriumDynamic equilibriumLe Chatelier's principle
Exam tips
- Use clear and precise language in explanations.: When explaining concepts like Le Chatelier's principle, use terms like 'shift' and 'counteract' to clearly convey how the system responds to changes.
- Use diagrams to illustrate equilibrium shifts: When explaining the effects of concentration changes, draw a diagram of the equilibrium position before and after the change.
Common mistakes
- Confusing static and dynamic equilibrium: Remember that in dynamic equilibrium, reactions are still occurring, but the rates are equal, maintaining constant concentrations.
- Confusing the effects of concentration changes: Remember that increasing the concentration of reactants shifts the equilibrium to the right, while increasing products shifts it to the left.
Practice preview
- Which of the following statements best describes dynamic equilibrium in a closed system?
- Explain how Le Chatelier's principle can be applied to predict the effect of increasing the concentration of a reactant in a reversible reaction.
- For the equilibrium reaction N2(g) + 3H2(g) ⇌ 2NH3(g), if the initial concentrations are [N2] = 0.5 mol/dm³ and [H2] = 1.5 mol/dm³, calculate the equilibrium constant Kc if at equilibrium [NH3] = 0.2 mol/dm³.
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