For which of the following reaction(s) is the enthalpy change for the reaction not equal to $\Delta$ H°_f of the product?
I. 2H(g) $\rightarrow$ H₂(g)
II. H₂(g) + O₂(g) $\rightarrow$ H₂O₂(l)
III. H₂O(l) + O(g) $\rightarrow$ H₂O₂(l)

Question

For which of the following reaction(s) is the enthalpy change for the reaction not equal to

\Delta

H°_f of the product?
I. 2H(g)

\rightarrow

H₂(g)
II. H₂(g) + O₂(g)

\rightarrow

H₂O₂(l)
III. H₂O(l) + O(g)

\rightarrow

H₂O₂(l)

Quizplus · Accepted Answer

The enthalpy change for a reaction is equal to the standard enthalpy of formation of the product only if the reactants are in their standard states. In reaction I, H(g) is not in its standard state (H₂(g) is), and in reaction III, O(g) is not in its standard state (O₂(g) is).

For Which of the Following Reaction(s) Is the Enthalpy Change Δ\DeltaΔ

For Which of the Following Reaction(s) Is the Enthalpy Change $\Delta$