Question

What is the standard enthalpy of formation of $NH_{3}$ gas?
$N_{2(g)}+3H_{2(g)}\to 2NH_{3(g)}; \Delta_{r}H^{\circ}=-92.4\,kJ\,mol^{-1}$

• A. $+46.2\,KJ\,mol^{-1}$
• B. $-46.2\,KJ\,mol^{-1}$
• C. $-36.5\,KJ\,mol^{-1}$
• D. $+36.5\,KJ\,mol^{-1}$

Answer 1

Answer: (B)

$N_{2(g)}+3H_{2(g)} \to 2NH_{3(g)} ; \Delta_{r}H^{\circ}=-92.4\,KJ\,mol^{-1}$
$\therefore $ Standard enthalpy of formation of $NH_{3(g)}$
$=\frac{-92.4}{2}$
$=-46.2\,kJ/mol$