Question

in the following reaction, what quantity in moles of $ch_{3}oh$ is required to give off 4221 kj of heat?
$2ch_{3}oh(l)+3o_{2}(g)\to 2co_{2}(g)+4h_{2}o$

Explanation:

Step1: Find the enthalpy change ($\Delta H$) for the reaction

Assume the standard enthalpy of combustion of \(CH_3OH\) is \(\Delta H=-1452\space kJ/mol\) (for \(2\space mol\) of \(CH_3OH\)).

Step2: Set up a proportion

Let \(n\) be the number of moles of \(CH_3OH\).
We have the proportion \(\frac{2\space mol}{1452\space kJ}=\frac{n}{4221\space kJ}\)

Step3: Solve for \(n\)

Cross - multiply: \(1452n = 2\times4221\)
\(n=\frac{2\times4221}{1452}\)
\(n = 5.8\space mol\)

Answer:

\(5.8\space mol\)