Question

determine the amount of no₂ produced, in g, if -552 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 \(\Delta H=- 114.6\space kJ/mol\) (per mole of reaction). If \(q = - 552\space kJ\) (heat given off), then moles of reaction \(n=\frac{q}{\Delta H}\).
\(n=\frac{-552\space kJ}{-114.6\space kJ/mol}\approx4.8168\space mol\)

Step2: Relate moles of reaction to moles of \(NO_2\)

From the balanced equation \(2NO(g)+O_2(g)\to2NO_2(g)\), for 1 mole of reaction, 2 moles of \(NO_2\) are produced. So moles of \(NO_2,n_{NO_2}=2\times n\)
\(n_{NO_2}=2\times4.8168 = 9.6336\space mol\)

Step3: Calculate mass of \(NO_2\)

Molar mass of \(NO_2\), \(M=(14 + 2\times16)\space g/mol=46\space g/mol\). Mass \(m = n_{NO_2}\times M\)
\(m=9.6336\space mol\times46\space g/mol = 443.1456\space g\approx443\space g\)

Answer:

\(443\space g\)