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Heat of Formation

APCHEM-EJMGEM

Consider the following table showing approximate bond energies.

Bond Bond Energy (kJ/mol)
N$\equiv$N 940
H$-$H 430
N$-$H 390

$\ $
The equation for the formation of gaseous ammonia, $N{ H }_{ 3 }(g)$, from the elements is shown below.

$${ N }_{ 2 }(g)+3{ H }_{ 2 }(g)\rightarrow 2N{ H }_{ 3 }(g)$$

Using the information given in the table, what is the molar heat of formation of ammonia (in kJ/mol $N{ H }_{ 3 }$)?

A

–110 kJ/mol $N{ H }_{ 3 }$

B

–55 kJ/mol $N{ H }_{ 3 }$

C

+55 kJ/mol $N{ H }_{ 3 }$

D

+110 kJ/mol $N{ H }_{ 3 }$