Zadanie 1b, Paper 1B, maj 2025, TZ3, Chemia IB SL
Wzorowane na: Chemistry SL Paper 1B, May 2025, TZ3, pytanie 1(b). Treść, dane i kontekst są zmienione; sprawdzane umiejętności, format i punktacja jak w oryginale.
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Zadanie
Wspólne informacje do wiązki zadań
Nitrogen dioxide, NO2, is a toxic and corrosive gas with a brown colour. Small quantities can be prepared in a school laboratory either by heating the nitrate of a group 2 metal, such as magnesium nitrate, or by reacting silver with concentrated nitric acid, HNO3. The gas prepared in this way was collected and sealed in a glass vessel, in which the following equilibrium is established:
2 NO2(g) ⇌ N2O4(g) ΔH⊖ = −57.2 kJ mol−1
Polecenie
The sealed vessel was left for the reaction to proceed. Suggest two properties of the system, other than its colour, that could be measured to follow the progress of the reaction over time, and predict how each would change as the forward reaction proceeds.
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Pokaż rozwiązanieUkryj rozwiązanieKlucz i punktacja
Odpowiedź z klucza
Property 1: temperature «of the gas mixture» ✔
Expected change: increases «because the forward reaction is exothermic» ✔
Property 2: pressure «inside the vessel, at constant volume» ✔
Expected change: decreases «because two moles of gas become one mole» ✔
OR
Property: absorbance in the IR/UV region «at a wavelength absorbed by NO2 or N2O4» ✔
Expected change: absorbance due to NO2 decreases / absorbance due to N2O4 increases ✔
Schemat punktowania
[1] for each measurable property (temperature; pressure at constant volume or volume at constant pressure; IR or UV absorbance) and [1] for the matching direction of change. A property given with the wrong direction earns [1 max] for that pair. Mass does not score, since it is constant in a sealed vessel; colour is excluded by the question.
Komentarz. Volume at constant pressure (decreasing) or gas density at constant pressure (increasing) are acceptable alternatives to pressure.