DP Chemistry (first assessment 2025)
Question 21M.2.HL.TZ2.7
| Date | May 2021 | Marks available | [Maximum mark: 6] | Reference code | 21M.2.HL.TZ2.7 |
| Level | HL | Paper | 2 | Time zone | TZ2 |
| Command term | Determine, State, State and explain | Question number | 7 | Adapted from | N/A |
7.
[Maximum mark: 6]
21M.2.HL.TZ2.7
Consider the following equilibrium reaction:
2SO2 (g) + O2 (g) 2SO3 (g)
(a)
State the equilibrium constant expression, Kc, for the reaction above.
[1]
Markscheme
«Kc = » ✓
Square brackets required for the mark.
(b)
State and explain how the equilibrium would be affected by increasing the volume of the reaction container at a constant temperature.
[3]
Markscheme
pressure decrease «due to larger volume» ✓
reaction shifts to side with more moles/molecules «of gas» ✓
reaction shifts left/towards reactants ✓
Award M3 only if M1 OR M2 awarded.
(c)
SO2 (g), O2 (g) and SO3 (g) are mixed and allowed to reach equilibrium at 600 °C.
Determine the value of Kc at 600 °C.
[2]
Markscheme
[O2] = 1.25 «mol dm−3» AND [SO3] = 3.50 «mol dm−3» ✓
«Kc ==» 4.36 ✓
Award [2] for correct final answer
Syllabus sections
Reactivity 2. How much, how fast and how far? » Reactivity 2.3—How far? The extent of chemical change » Reactivity 2.3.2—The equilibrium law describes how the equilibrium constant, K, can be determined from the stoichiometry of a reaction. Deduce the equilibrium constant expression from an equation for a homogeneous reaction.
Reactivity 2. How much, how fast and how far? » Reactivity 2.3—How far? The extent of chemical change » Reactivity 2.3.4—Le Châtelier’s principle enables the prediction of the qualitative effects of changes in concentration, temperature and pressure to a system at equilibrium. Apply Le Ch.telier’s principle to predict and explain responses to changes of systems at equilibrium.
Reactivity 2. How much, how fast and how far? » Reactivity 2.3—How far? The extent of chemical change » Reactivity 2.3.6—The equilibrium law is the basis for quantifying the composition of an equilibrium mixture. Solve problems involving values of K and initial and equilibrium concentrations of the components of an equilibrium mixture.