Equilibria — WJEC A-Level Chemistry
In summary: Equilibria is a key topic in WJEC A-Level Chemistry. Key exam tip: Always check the stoichiometry of the balanced equation before writing the expression for Kc or Kp
Exam Tips for Equilibria
- Always check the stoichiometry of the balanced equation before writing the expression for Kc or Kp
- Ensure units are calculated correctly for every equilibrium constant expression
- Use a pH probe for titration practicals to obtain accurate data for curve plotting
- Practice converting between pH, [H+], Ka, and pKa fluently
- Remember that Kw is temperature dependent
Common Mistakes
- Incorrectly identifying the effect of temperature on the value of equilibrium constants
- Confusing the units for Kp and Kc or failing to include them
- Errors in logarithmic calculations for pH and pKa
- Misinterpreting the magnitude of K as a direct measure of reaction rate
- Failing to account for stoichiometry in equilibrium expressions
- Incorrectly identifying the components of a buffer solution
Marking Points
- Effect of temperature on Kp and Kc for exothermic and endothermic reactions
- Calculation of Kp and Kc values and equilibrium quantities from given data
- Significance of the magnitude of an equilibrium constant regarding the position of equilibrium
- Lowry-Bronsted theory of acids and bases
- Differences between strong and weak acids/bases using acid dissociation constant (Ka)
- Ionic product of water (Kw)
- Calculations involving pH, Kw, Ka, and pKa for strong and weak acids/bases
- Shapes of titration curves for various acid-base combinations
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