Zacznij za darmoZacznij

Zadanie 2c

4 pktobliczenioweśrednie (szac.)Paper 2, maj 2026, TZ3

Wzorowane na: Chemistry HL Paper 2, May 2026, TZ3, pytanie 2(c). Treść, dane i kontekst są zmienione; sprawdzane umiejętności, format i punktacja jak w oryginale.

Zapisz zadanie

Darmowe konto pozwoli wrócić do niego później.

Informacja do zadań 2a-2c.

Sulfur dioxide, SO2, is a covalently bonded compound and a common air pollutant released when sulfur-containing fuels burn.

Polecenie

Nitrogen monoxide reacts with chlorine in the atmosphere:

2 NO(g) + Cl2(g) → 2 NOCl(g)

The rate equation was determined experimentally as Rate = k[NO]2[Cl2].

(i) A student proposed the following mechanism and suggested that Step 1 was the rate-determining step.

Step 1: NO(g) + Cl2(g) → NOCl2(g)

Step 2: NOCl2(g) + NO(g) → 2 NOCl(g)

Evaluate the proposed mechanism and the rate-determining step.

(ii) Calculate the value and the units of the rate constant, k, using these data from one experiment.

[NO] / mol dm−3[Cl2] / mol dm−3Rate / mol dm−3 s−1
2.5 × 10−21.8 × 10−24.5 × 10−5
Sprawdź rozwiązanieUkryj rozwiązanieKlucz CKE i punktacja

Zanim porównasz z kluczem

Jak poszło Ci z tym zadaniem?

Wybierz ocenę: zapisze wynik i od razu oznaczy zadanie jako zrobione.

ŁatweŚrednieTrudne

Zapis wymaga darmowego konta. Załóż konto

Odpowiedź z klucza

(i) the two steps add up to the overall equation 2 NO + Cl2 → 2 NOCl «NOCl2 is an intermediate», so the mechanism is consistent with the stoichiometry ✔

Step 1 cannot be the rate-determining step, because it would give Rate = k[NO][Cl2], first order in NO «not second order»;

Step 2 is the rate-determining step «with Step 1 a fast equilibrium», which gives Rate = k[NO]2[Cl2] ✔

(ii) «k=rate[NO]2[ClX2]=4.5×10−5(2.5×10−2)2×1.8×10−2=k = \dfrac{\mathrm{rate}}{[\ce{NO}]^2[\ce{Cl2}]} = \dfrac{4.5 \times 10^{-5}}{(2.5 \times 10^{-2})^2 \times 1.8 \times 10^{-2}} =» 4.0 ✔

mol−2 dm6 s−1 ✔

Schemat punktowania

(i) M1: the steps sum to the overall equation, so the mechanism is consistent with the stoichiometry; M2: Step 1 is rejected as the rate-determining step because it would give a rate equation first order in NO, AND Step 2 is identified as the slow step (accept "Step 1 is a fast equilibrium"). Do not award M2 for the bare statement that the student is wrong. (ii) Award [2] for the correct value with correct units; [1] for the value and [1] for the units.

Komentarz

The intermediate NOCl2 forms from one NO and one Cl2, and Step 2 adds the second NO, so a slow Step 2 after a fast Step 1 reproduces the experimental rate equation.

Umiejętności w zadaniu