Q35 · Practice questionComplex familiar4 marks
QUESTION 35 (4 marks)
The graph shows in a constant-volume vessel. Only the temperature is increased at min. The solid line is B and the dashed line is A.
a) State the evidence that the mixture was initially at equilibrium. [1 marks]
b) Determine the sign of the forward reaction enthalpy change and explain. [2 marks]
c) Determine whether the equilibrium constant increases or decreases. [1 marks]
WORKED SOLUTION
4 marksPractice marking scheme
a) Constant concentrations. b) Positive; endothermic. c) Increases.
The initial concentrations are constant. Heating increases B and decreases A, favouring the forward reaction; it is endothermic. Since Kc=[B]/[A], the larger final ratio means Kc increases.
- Identifies constant concentrations initially. [1 marks]
- Identifies endothermic/positive ΔH. [1 marks]
- Explains heating favours formation of B. [1 marks]
- States Kc increases. [1 marks]
Practice question aligned to the current QCAA syllabus; review the worked solution and marking criteria.
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