Answer:
In none of the reactions ΔH°rxn equal to ΔH°f of the product.
Explanation:
The standard enthalpy of formation (ΔH°f) is the enthalpy change when 1 mole of a product is formed from its constituent elements in the standard states.
1/2 O₂(g) + H₂O(g) ⟶ H₂O₂(g)
ΔH°rxn is NOT equal to ΔH°f of the product because H₂O(g) is not an element but a compound.
Na⁺(g) + F⁻(g) ⟶ NaF(s)
ΔH°rxn is NOT equal to ΔH°f of the product because Na and F are not in their standard states (Na(s); F₂(g)).
K(g) + 1/2 Cl₂(g) ⟶ KCl(s)
ΔH°rxn is NOT equal to ΔH°f of the product because K is not in its standard state (K(s)).
O₂(g) + 2 N₂(g) ⟶ 2 N₂O(g)
ΔH°rxn is NOT equal to ΔH°f of the product because 2 moles of N₂O are formed.
In none of the above ΔHrxn equal to ΔHf of the product.