Question

question 2 (1 point)
which equation would you use to determine the standard enthalpy change for the following reaction?
2 nh3(g) → n2(g) + 3 h2(g)
the standard enthalpy of formation of nh3 is -45.9 kj/mol.
δh_reaction ≅ δu_reaction + rtδn_gases
δe_rxn = σbe_(bonds broken) - σbe_(bonds formed)
-(m_sys × c_sys × δt_sys) = (m_surr × c_surr × δt_surr)
δh°_reaction = σδh°_f products - σδh°_f reactants

Explanation:

The standard enthalpy change of a reaction ($\Delta H^{\circ}_{reaction}$) can be calculated using the standard enthalpies of formation ($\Delta H^{\circ}_{f}$) of the products and reactants. The formula $\Delta H^{\circ}_{reaction}=\sum\Delta H^{\circ}_{f\text{ products}}-\sum\Delta H^{\circ}_{f\text{ reactants}}$ is the correct one for this purpose. The first option relates internal - energy change to enthalpy change, the second is for bond - energy calculations, and the third is for heat - transfer between system and surroundings.

Answer:

$\Delta H^{\circ}_{reaction}=\sum\Delta H^{\circ}_{f\text{ products}}-\sum\Delta H^{\circ}_{f\text{ reactants}}$