# How do you use Hess's Law to calculate enthalpy for this reaction?

## Given Data: $\text{N"_2(g) + "O"_2(g) -> 2"NO} \left(g\right)$ $\Delta H = + \text{180.7 kJ}$ $2 {\text{NO"(g) + "O"_2(g) -> 2"NO}}_{2} \left(g\right)$ $\Delta H = - \text{113.1 kJ}$ $2 {\text{N"_2"O"(g) -> 2"N"_2(g) + "O}}_{2} \left(g\right)$ $\Delta H = - \text{163.2 kJ}$ Use Hess' Law to calculate $\Delta H$ for the reaction: $\text{N"_2"O"(g) + "NO"_2(g) -> 3"NO} \left(g\right)$

Mar 31, 2018

ΔH = 311.3 $\text{kJ}$

#### Explanation:

PC of cake

${\cancel{\text{N}}}_{2}$ + ${\cancel{\text{O}}}_{2}$ $\text{ ----->}$ $2 N O$

$2 N {O}_{2}$ $\text{ ----->}$ $2 N O$ + ${\cancel{\text{O}}}_{2}$

$2 {N}_{2} O$ $\text{ ----->}$ $\cancel{\text{2}} {N}_{2}$ + ${O}_{2}$
$\text{---------------------------------}$

$2 N {O}_{2}$ + $2 {N}_{2} O$ $\text{ -----> }$$4 N O$ + ${\cancel{\text{N}}}_{2}$ + ${\cancel{\text{O}}}_{2}$

${\cancel{\text{N}}}_{2}$ + ${\cancel{\text{O}}}_{2}$ $\text{ -----> }$$2 N O$
$\text{---------------------------------}$
$N {O}_{2}$ + ${N}_{2} O$ $\text{ -----> }$$3 N O$
"=>180.7 113.1 + (- 163.2) + 180.7 = 311.3 kJ