Question

determine the amount of no₂ produced, in g, if -744 kj of heat is given off, according to the following equation:
2 no(g) + o₂(g) → 2 no₂(g)
δh = -114.6 kj/mol
report your answer to the nearest whole number.

Explanation:

Step1: Calculate moles of reaction

Given $\Delta H=- 114.6\ \text{kJ/mol}$, heat given off $q = - 744\ \text{kJ}$.
Number of moles of reaction $n=\frac{q}{\Delta H}=\frac{-744\ \text{kJ}}{-114.6\ \text{kJ/mol}}\approx6.49\ \text{mol}$

Step2: Relate moles of reaction to moles of $NO_2$

From the equation $2NO(g)+O_2(g)\to2NO_2(g)$, for each mole of reaction, 2 moles of $NO_2$ are produced.
Moles of $NO_2,n_{NO_2}=2\times n = 2\times6.49\ \text{mol}=12.98\ \text{mol}$

Step3: Calculate mass of $NO_2$

Molar mass of $NO_2,M=(14 + 2\times16)\ \text{g/mol}=46\ \text{g/mol}$
Mass of $NO_2,m = n_{NO_2}\times M=12.98\ \text{mol}\times46\ \text{g/mol}=597.08\ \text{g}\approx597\ \text{g}$

Answer:

$597$