From the following data at 25°C, which of the following statement(s) is/are correct? (one or more than one correct)
1/2 N₂(g) + 1/2 O₂(g) → NO(g); ΔH° = 90 kJ
N₂(g) + 2O₂(g) → 2NO₂(g); ΔH° = 66 kJ
N₂(g) → 2N(g); ΔH° = 946 kJ
O₂(g) → 2O(g); ΔH° = 498 kJ

Question

From the following data at 25°C, which of the following statement(s) is/are correct? (one or more than one correct)

1/2 N₂(g) + 1/2 O₂(g) → NO(g); ΔH° = 90 kJ

N₂(g) + 2O₂(g) → 2NO₂(g); ΔH° = 66 kJ

N₂(g) → 2N(g); ΔH° = 946 kJ

O₂(g) → 2O(g); ΔH° = 498 kJ

TestHub · Accepted Answer

Δ f H(N) = 946/2 = 473 kJ/mol and Δ f H(O) = 498/2 = 249 kJ/mol; Δ f H(NO 2 ) = 66/2 = 33 kJ/mol. (a) NO → 1/2 N 2 + 1/2 O 2 (-90), then N (+473) and O (+249): -90 + 473 + 249 = 632 kJ, not 812 (false). (b) True. (c) The 66 kJ is for 2 mol NO 2 , so the formation enthalpy is 33 kJ/mol (false). (d) ΔH = Δ f H(NO) - Δ f H(NO 2 ) = 90 - 33 = +57 kJ (true). Ans (b),(d).

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