Question

For which one of the following is the enthalpy of the reaction the same as the enthalpy of formation?

A) 2 Fe (s) + 3/2 O2 → (g) Fe2O(s)

B) HCl(aq) + NH3 (g) → NH4Cl (s)

C) AsF3 (s) → As (s) + 3/2 F2 (g)

D) N2(g) + 3 H2(g) → 2 NH3 (g)

Answer 1

The enthalpy of formation is the same as the enthalpy of the reaction in option D) N2(g) + 3 H2(g) → 2 NH3 (g).

Step-by-step explanation:

The enthalpy of formation refers to the enthalpy change that occurs when one mole of a compound is formed from its constituent elements in their standard states. It can be calculated by summing the enthalpies of the formation of the reactants and subtracting the enthalpies of the formation of the products. In the given options, the enthalpy of the reaction is the same as the enthalpy of formation for option D) N2(g) + 3 H2(g) → 2 NH3 (g).

Answer 2

The enthalpy of reaction is the same as the enthalpy of formation for option (A) 2 Fe (s) + 3/2 O2 (g) → Fe2O3 (s), as it represents the formation of 1 mole of iron(III) oxide from its elements in their standard states.

Step-by-step explanation:

The student is asking about the enthalpy change for a formation reaction, which is known as the enthalpy of formation. The enthalpy of formation represents the enthalpy change when 1 mole of a compound is formed from its elements in their standard states. For a reaction to represent the enthalpy of formation, it must form a compound from its constituent elements in their standard states, with the product being 1 mole of that compound.

Given the options, (A) 2 Fe (s) + 3/2 O2 (g) → Fe2O3 (s) is the reaction that represents the enthalpy of formation for iron(III) oxide, with iron and oxygen in their standard states combining to form exactly 1 mole of iron(III) oxide, Fe2O3. Hence, the enthalpy change for this reaction (ΔH) would be the same as the enthalpy of formation (ΔHf) for Fe2O3(s).