Zadanie 16
Wzorowane na: Chemistry SL Paper 1A, May 2026, TZ3, pytanie 16. Treść, dane i kontekst są zmienione; sprawdzane umiejętności, format i punktacja jak w oryginale.
Darmowe konto pozwoli wrócić do niego później.
Polecenie
The enthalpy change for the combustion of propane is calculated from bond enthalpy data and compared with the literature value.
C3H8(g) + 5 O2(g) → 3 CO2(g) + 4 H2O(l)
| From bond enthalpy values, ΔH / kJ mol−1 | Literature value, ΔH⊖ / kJ mol−1 |
|---|---|
| -2034 | -2219 |
Which statement best explains why the calculated value is less negative than the literature value?
A. Bond enthalpy values refer to liquid water, so the energy released in forming the O-H bonds is overestimated
B. Breaking the bonds in propane and oxygen releases energy, which the calculation leaves out
C. Bond enthalpy values refer to gaseous species, so the energy released when water vapour condenses to liquid water is not included
D. The literature value refers to all of the species in the gaseous state
Sprawdź rozwiązanieUkryj rozwiązanieKlucz CKE i punktacja
Odpowiedź z klucza
C ✔
«bond enthalpies describe gaseous species, so the calculation behaves as if water were produced as vapour; condensing H2O(g) to H2O(l) releases further energy that only the literature value includes, making it more negative»
Schemat punktowania
1 mark for the correct option.
Komentarz
Bond breaking always absorbs energy, so a calculation that omits it would give a value that is too negative, not too small in magnitude.