Zadanie 14a
Wzorowane na: Chemistry HL Paper 3, November 2024, pytanie 14(a). Treść, dane i kontekst są zmienione; sprawdzane umiejętności, format i punktacja jak w oryginale.
Darmowe konto pozwoli wrócić do niego później.
Polecenie
Petrol (gasoline) is a mixture of hydrocarbons and can be blended with bioethanol. The carbon footprint of a fuel can be expressed as the mass of carbon dioxide, in kg, produced per kg of fuel burned.
(i) Calculate the carbon footprint of heptane, C7H16, in kg of CO2 per kg of heptane burned, assuming complete combustion.
(ii) State a reason why replacing part of the petrol with bioethanol lowers the net amount of carbon dioxide added to the atmosphere.
Sprawdź rozwiązanieUkryj rozwiązanieKlucz i punktacja
Odpowiedź z klucza
(i) C7H16(l) + 11 O2(g) → 7 CO2(g) + 8 H2O(g) ✔
«Mr(C7H16) = 100.23, so 1 kg is 9.977 mol and gives 69.84 mol of CO2»
«» 3.07 «kg CO2 per kg heptane» ✔
(ii) the carbon dioxide released when the ethanol burns was absorbed from the atmosphere by the crops «by photosynthesis» when they grew ✔
Schemat punktowania
(i) M1: balanced equation (whole-number coefficients also accepted: 2C7H16 + 22O2 → 14CO2 + 16H2O). M2: final answer, 3.07 (3.08 if whole-number molar masses are used). Award [2] for the correct final answer. (ii) Do not accept 'renewable' or 'carbon neutral' without the explanation.