Final answer:
The correct standard heat of reaction (ΔH°) for the formation of ammonia from nitrogen and hydrogen, based on the standard heats of formation, is -92.4 kJ/mol. The correct expression is 2(-46.2 kJ/mol) - [0 + 3(0)].
Step-by-step explanation:
The standard heat of reaction (ΔH°) can be calculated using the standard heats of formation (ΔH°f) for the reactants and products involved in a chemical reaction. This is known as Hess's Law, which states that the total enthalpy change for a reaction is the sum of the enthalpy changes for the individual steps into which the reaction can be divided. The standard heat of reaction is calculated by subtracting the sum of the heats of formation of the reactants from the sum of the heats of formation of the products.
The general formula to calculate the standard heat of reaction is:
ΔH° = ∑ΔH°f (products) - ∑ΔH°f (reactants)
The question appears to have a typo in the mentioned reaction. Assuming the given reaction is the formation of ammonia (NH₃) from nitrogen (N₂) and hydrogen (H₂):
N₂(g) + 3H₂(g) → 2NH₃(g)
The correct expression to calculate ΔH° for the formation of ammonia, based on the provided standard heats of formation, should then be:
ΔH° = 2(ΔH°f [NH₃(g)]) - [ΔH°f [N₂(g)] + 3(ΔH°f [H₂(g)])]
Since ΔH°f for elemental substances like N₂ and H₂ in their standard states is zero, and given the ΔH°f for NH₃(g) is -46.2 kJ/mol, the calculation is:
ΔH° = 2(-46.2 kJ/mol) - [0 + 3(0)]
ΔH° = -92.4 kJ/mol
Therefore, the correct mathematical expression is (b) 2(-46.2) - [3(0) + 0], resulting in -92.4 kJ/mol.