Question

question 9
determine the amount of heat, in kj, given off when 258 g of no₂ is produced 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, and be sure to include the correct sign.

Explanation:

Step1: Calculate the molar mass of \(NO_2\)

The molar mass of \(N = 14\space g/mol\) and \(O=16\space g/mol\). For \(NO_2\), \(M=(14 + 2\times16)\space g/mol=46\space g/mol\)

Step2: Calculate the number of moles of \(NO_2\)

Using the formula \(n=\frac{m}{M}\), where \(m = 258\space g\) and \(M = 46\space g/mol\). So \(n=\frac{258}{46}\space mol\approx5.6087\space mol\)

Step3: Calculate the heat released

From the equation \(2NO(g)+O_2(g)\to2NO_2(g)\), \(\Delta H=- 114.6\space kJ/mol\) (per 2 - mole \(NO_2\) produced). For \(n = 5.6087\space mol\) of \(NO_2\), the heat \(q\) is calculated as follows.
Since for 2 moles of \(NO_2\), \(\Delta H=-114.6\space kJ\). For \(n\) moles of \(NO_2\), \(q=\frac{- 114.6}{2}\times n\)
Substitute \(n = 5.6087\) into the formula: \(q=\frac{-114.6}{2}\times5.6087=- 320.9\space kJ\approx - 321\space kJ\)

Answer:

\(-321\)