Zadanie 2a
Wzorowane na: Chemistry HL Paper 2, May 2026, TZ3, pytanie 2(a). Treść, dane i kontekst są zmienione; sprawdzane umiejętności, format i punktacja jak w oryginale.
Darmowe konto pozwoli wrócić do niego później.
Informacja do zadań 2a-2c.
Sulfur dioxide, SO2, is a covalently bonded compound and a common air pollutant released when sulfur-containing fuels burn.
Polecenie
(i) Sulfur dioxide is oxidized to sulfur trioxide by nitrogen dioxide in the atmosphere. Determine the enthalpy change, ΔH⊖, in kJ mol−1, for the reaction SO2(g) + NO2(g) → SO3(g) + NO(g) given these reactions and enthalpy values:
2 SO2(g) + O2(g) → 2 SO3(g) ΔH⊖ = −197.8 kJ mol−1
2 NO(g) + O2(g) → 2 NO2(g) ΔH⊖ = −114.2 kJ mol−1
(ii) Suggest the value of the bond angle and the molecular geometry of sulfur dioxide based on the Lewis formula shown below.
(iii) Calculate the volume, in dm3, of 1.35 mol of sulfur dioxide gas at 62.0 °C and 108 kPa. Use sections 1 and 2 of the data booklet.
(iv) Explain one reason why real gases such as sulfur dioxide deviate from the behaviour of an ideal gas.
(v) Annotate the Lewis formula of sulfur dioxide from part (ii) with formal charges.
Sprawdź rozwiązanieUkryj rozwiązanieKlucz CKE i punktacja
Odpowiedź z klucza
(i) «reaction 1 halved:» −197.8/2 = −98.9 AND «reaction 2 halved and reversed:» +114.2/2 = +57.1 ✔
«−98.9 + 57.1 =» −41.8 kJ mol−1 ✔
(ii) Bond angle: 110° ≤ angle < 120° «actual value 119°» ✔
Molecular geometry: bent / V-shaped / angular ✔
(iii) «V = nRT/P = (1.35 × 8.31 × 335)/108 =» 34.8 dm3 ✔
(iv) at high pressure the volume of the molecules is not negligible compared with the volume of the container
OR
at low temperature the intermolecular forces / attractions between molecules cannot be ignored ✔
(v) left O (double bond) 0 AND S +1 AND right O (single bond) −1 ✔
Schemat punktowania
(i) Award [2] for the correct final answer. M1: both enthalpy values halved with the correct signs (the second reversed); M2: sum. (ii) [1] for each; accept any angle from 110° to 119°; accept "angular" or "V-shaped". (iii) [1]; temperature must be converted to 335 K and pressure left in kPa to give dm3. (iv) [1]: a condition together with the matching reason; accept either alternative. (v) [1]: all three charges must be correct and on the right atoms.
Komentarz
The lone pair on sulfur counts as an electron domain: three domains give an angle a little below 120° and a bent, not linear, shape.