Zadanie 4b
Wzorowane na: Chemistry SL Paper 2, May 2024, TZ1, pytanie 4(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 4a-4b.
Carbonyl chloride (phosgene), COCl2, is made industrially from carbon monoxide and chlorine over a charcoal catalyst:
CO(g) + Cl2(g) → COCl2(g) ΔH = −108 kJ mol−1
Polecenie
(i) Draw the Lewis (electron dot) structure of carbonyl chloride.
(ii) Mark the bond polarities on your Lewis structure using the symbols δ+ and δ−.
(iii) Explain the shape of the carbonyl chloride molecule and whether it is polar.
(iv) Outline why the rising concentration of carbon dioxide in the atmosphere, produced mainly by the burning of fossil fuels, matters to every country and not only to those that emit the most.
(v) The enthalpy level diagram shows the reaction . Explain, referring to the diagram, whether nitrogen monoxide is more or less stable than nitrogen dioxide.
Sprawdź rozwiązanieUkryj rozwiązanieKlucz i punktacja
Odpowiedź z klucza
(i) carbon in the centre joined to oxygen by a double bond and to two chlorine atoms by single bonds; two lone pairs on oxygen and three lone pairs on each chlorine ✔
(ii) δ+ on carbon AND δ− on oxygen AND δ− on each chlorine ✔
(iii) trigonal planar AND three electron domains repel each other «to a maximum separation» ✔
polar AND bond dipoles do not cancel / asymmetric distribution of charge ✔
(iv) carbon dioxide is a greenhouse gas / absorbs infrared radiation «emitted by the Earth's surface» ✔
a rising concentration enhances the greenhouse effect, causing global warming / climate change «which affects the whole planet, because the gas mixes throughout the atmosphere regardless of where it is emitted» ✔
(v) nitrogen monoxide is less stable «than nitrogen dioxide» AND is at a higher enthalpy than NO2 / energy is released when NO is oxidized to NO2 ✔
Schemat punktowania
(i) [1]; dots, crosses and lines are all acceptable in any combination; the shape of the drawing is not marked. (ii) [1]; accept the polarity marked correctly on only one of the bonds, or on all three. (iii) Award [1] for "trigonal planar and polar" without correct explanations. (iv) M1: carbon dioxide absorbs infrared radiation or acts as a greenhouse gas; M2: global warming or climate change, with the idea that the effect is not local; accept ocean acidification for M2. (v) [1]: the conclusion (NO is less stable) must be supported by the relative enthalpy levels or by the release of energy; the conclusion alone earns nothing.
Komentarz
In (v), stability is judged by enthalpy: the species or system at the lower enthalpy is the more stable one.