Chemistry - Thermochemistry Question with Solution | TestHub

Question Explanation:

Match the given reactions with the reason for them not representing a standard enthalpy of formation.

Concept:

Standard Enthalpy of Formation.

Solution:

Standard enthalpy of formation requires one mole of product formed from elements in their standard states.

A. H₂(g) + Br₂(l) → 2HBr(g): Forms 2 moles of product. → q (Stoichiometric coefficients)

B. $\frac{1}{2}$I₂(s) + $\frac{1}{2}$Br₂(l) → IBr(s): Forms 1 mole of product from elements in standard states.

This does represent standard enthalpy of formation. → s (No defect)

C. CO₂(g) + 2H₂(g) → 2H₂O(l): Reactant CO₂(g) is a compound. → r (Elements are not in standard state/Reactant is a compound)

D. S(monoclinic) + O₂(g) → SO₂(g): S(monoclinic) is not the standard state of sulfur (Sᵣₕₒₘᵦᵢ꜀). →P (Elements are not in standard state)