Question

determine the amount of no₂ produced, in g, if -200 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 released $q = - 200\ \text{kJ}$.
Number of moles of reaction $n=\frac{q}{\Delta H}=\frac{-200\ \text{kJ}}{-114.6\ \text{kJ/mol}}\approx1.745\ \text{mol}$

Step2: Calculate moles of $\text{NO}_2$

From the balanced equation $2\text{NO}(g)+\text{O}_2(g)\to2\text{NO}_2(g)$, for each mole of reaction, 2 moles of $\text{NO}_2$ are produced.
Moles of $\text{NO}_2,n_{\text{NO}_2}=2\times n = 2\times1.745\ \text{mol}=3.49\ \text{mol}$

Step3: Calculate mass of $\text{NO}_2$

Molar mass of $\text{NO}_2,M=(14 + 2\times16)\ \text{g/mol}=46\ \text{g/mol}$
Mass of $\text{NO}_2,m = n_{\text{NO}_2}\times M=3.49\ \text{mol}\times46\ \text{g/mol}\approx160\ \text{g}$

Answer:

$160$