Zadanie 5b
Wzorowane na: Chemistry HL Paper 2, May 2026, TZ2, pytanie 5(b). Treść, dane i kontekst są zmienione; sprawdzane umiejętności, format i punktacja jak w oryginale.
Darmowe konto pozwoli wrócić do niego później.
Informacja do zadań 5a-5b.
Bromine atoms released from halogenated compounds destroy ozone in the stratosphere in a cycle of two reactions.
Br ∙ (g) + O3(g) → BrO ∙ (g) + O2(g)
BrO ∙ (g) + BrO ∙ (g) → 2 Br ∙ (g) + O2(g)
| Species | ΔHf⊖ / kJ mol−1 |
|---|---|
| Br ∙ (g) | 111.9 |
| BrO ∙ (g) | 125.8 |
| O3(g) | 142.7 |
Polecenie
Use bond enthalpies to calculate the enthalpy change, in kJ mol−1, for the first reaction.
Br ∙ (g) + O3(g) → BrO ∙ (g) + O2(g)
Use section 12 of the data booklet and the table below.
| Bond | Bond enthalpy / kJ mol−1 |
|---|---|
| Between Br and O in the BrO molecule | 235 |
| Between O and O in the O3 molecule | 302 |
Sprawdź rozwiązanieUkryj rozwiązanieKlucz CKE i punktacja
Odpowiedź z klucza
«bonds broken =» 2(302) / 604 «kJ mol−1» ✔
«bonds formed =» 235 + 498 / 733 «kJ mol−1» ✔
«ΔH = bonds broken − bonds formed = 604 − 733 =» −129 «kJ mol−1» ✔
Schemat punktowania
[3] M1 bonds broken; M2 bonds formed, using 498 for O=O from section 12; M3 enthalpy change. Award [3] for a correct final answer.
Komentarz
Both O–O bonds of ozone are broken, because one oxygen atom ends up in BrO and the other two form the new O=O bond. The result agrees with −128.8 kJ mol-1 from formation enthalpies, 125.8 − (111.9 + 142.7).