Using Hess's law, what is ΔH°_rxn for the following reaction? NO(g) + O(g) → NO₂(g) A) -839.8 kJ/mol B) -306.0 kJ/mol C) 157.9 kJ/mol D) 394.9 kJ/mol E) 442.3 kJ/mol

Question

Quizplus · Accepted Answer

Using Hess's law, we can calculate the ΔH° for a reaction by breaking it down into a series of smaller reactions with known ΔH° values. We can start with the given reaction: NO(g) + O(g) → NO₂(g) ΔH° = ? We can break this down into the following two reactions: NO(g) + ½O2(g) → NO2(g) ΔH° = -183.5 kJ/mol (known) NO2(g) + ½O2(g) → NO₂(g) ΔH° = ? Notice that the second reaction is the formation of NO₂(g) from its elements, so its ΔH° is simply the standard enthalpy of formation of NO₂(g), which is also a known value: N2(g) + O2(g) → 2NO(g) ΔH° = +180.6 kJ/mol (known) ½N2(g) + O2(g) + ½S(s) → NO₂(g) ΔH°f° = -83.5 kJ/mol (known) Finally, we can use Hess's law to calculate the ΔH° of the original reaction: ΔH° = ΔH°f°(NO₂(g)) - [ΔH°(NO2(g)) + ΔH°(½O2(g))] = -83.5 kJ/mol - [-183.5 kJ/mol + 0 kJ/mol] = -83.5 kJ/mol + 183.5 kJ/mol = 100.0 kJ/mol Therefore, the answer is B) -306.0 kJ/mol.

Using Hess's Law, What Is ΔH°rxn for the Following Reaction

Using Hess's Law, What Is ΔH°_rxn for the Following Reaction