Work through the list without notes. If you cannot do a statement, follow its link, then come back. Guide = study guide; Practice = practice questions.
Understanding
- I can say what information I need to predict equilibrium concentrations: the balanced equation, the initial values and K. (Guide: “The question this topic answers”)
- I can explain what happens next when Q < K, Q > K and Q = K. (Guide: “Step 1: compare Q with K”; Practice Q1)
- I can describe dynamic equilibrium as equal forward and reverse rates, with constant (not equal) concentrations. (Guide: “What ‘at equilibrium’ really means”; Practice Q4)
- I can explain why a mixture that starts with only products must react backwards. (Practice Q5)
Calculation
- I can convert moles and volume into concentrations before using Kc. (Guide: Worked example 2; Practice Q6)
- I can write an ICE table with changes in the ratio of the coefficients and the correct signs. (Guide: “Step 2: the ICE table”; Practice Q2)
- I can solve a perfect-square K expression by taking the square root. (Guide: Worked example 1; Practice Q5)
- I can use the small-x shortcut when K is very small and check that x is under about 5% of the starting value. (Guide: Worked example 2; Practice Q3)
- I can solve a quadratic when no shortcut works and reject the root that gives a negative concentration. (Practice Q6(c))
- I can handle a very large K by going to completion and letting a small amount come back. (Practice Q7)
- I can check my answers by substituting them back into K, and by checking that atoms balance. (All worked examples; Practice Q5)
Skills and reasoning
- I can sketch a concentration–time graph with a labelled, evenly scaled axis, curves in the ratio of the coefficients and a common levelling-off time. (Guide: Figure 1; Practice Q6(d))
- I can explain why the small-x shortcut fails when it gives an impossible value of x. (Practice Q6(b))
All ticked? Move on to Topic 7.8, Representations of Equilibrium, or return to the course roadmap.