Zadanie 4c
Wzorowane na: Chemistry SL Paper 2, May 2024, TZ2, pytanie 4(c). 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-4c.
Propenal, CH2=CHCHO, is a reactive liquid that serves as an intermediate in the making of pharmaceuticals.
Polecenie
Propenal can be made by the dehydration of propane-1,2,3-triol (glycerol):
CH2(OH)CH(OH)CH2OH(l) → CH2=CHCHO(g) + 2 H2O(g)
Two related reactions were studied separately.
Reaction 1: CH2(OH)CH(OH)CH2OH(l) → HOCH2CH2CHO(g) + H2O(g) ΔH⊖ = +87 kJ mol−1
Reaction 2: CH2=CHCHO(g) + H2O(g) → HOCH2CH2CHO(g) ΔH⊖ = −31 kJ mol−1
(i) Use Reactions 1 and 2 to calculate the standard enthalpy change for the dehydration of glycerol to propenal.
(ii) Sketch a potential energy profile for the dehydration in (i), with labelled axes (energy and progress of reaction), and mark on it the enthalpy change and the activation energy.
Sprawdź rozwiązanieUkryj rozwiązanieKlucz i punktacja
Odpowiedź z klucza
(i) Reaction 2 is reversed, giving HOCH2CH2CHO(g) → CH2=CHCHO(g) + H2O(g) with ΔH⊖ = +31 kJ mol−1, and added to Reaction 1 ✔
«ΔH⊖ = +87 + 31 =» +118 kJ mol−1 ✔
(ii) diagram with the products higher in energy than the reactants (endothermic) and a labelled arrow showing ΔH between the two levels ✔
labelled arrow showing Ea from the reactants to the top of the curve ✔
Schemat punktowania
(i) Award [2] for the correct final answer. M1: Reaction 2 reversed (its sign changed) before the two reactions are combined; M2: +118. Award [1] for +56 (Reaction 2 not reversed) and [1] for -118 (sign error). (ii) M1: endothermic profile with ΔH marked; M2: Ea marked from the reactants to the maximum.