Chapter 15.3, Problem 29SSC

Interpretation Introduction

Interpretation:

The heat released on combustion of 206g of hydrogen gas is to be determined.

Concept introduction:

Enthalpy of combustion: It is the amount of heat produced when one mole of a substance burns completely in oxygen.

Answer to Problem 29SSC

Mass of hydrogen gas $m=206g$

Enthalpy of combustion ( $\Delta H_{comb}$ ) for hydrogen gas $=-286\raisebox{1ex}{$kJ$}\!\left/ \!\raisebox{-1ex}{$mol$}\right.$

Molar mass of hydrogen ${\mathrm{H}}_2=1\times 2=2\raisebox{1ex}{$g$}\!\left/ \!\raisebox{-1ex}{$mol$}\right.$

Number of moles in 206g of hydrogen gas $\mathrm{N}=\frac{206g}{2\raisebox{1ex}{$g$}\!\left/ \!\raisebox{-1ex}{$mol$}\right.}=103mol$

$\begin{array}{l}Q=\mathrm{N}\times \Delta H_{comb}\\ Q=103mol\times -286\raisebox{1ex}{$kJ$}\!\left/ \!\raisebox{-1ex}{$mol$}\right.\\ Q=-29458kJ\end{array}$

Explanation of Solution

The following steps are needed to calculate the heat released:

• Calculate the molar mass of hydrogen gas
• Calculate the number of moles in 206g of hydrogen gas.
• Calculate the heatreleased on combustion using the formula,

$Q=\mathrm{N}\times \Delta H_{comb}$

Conclusion

206 g of hydrogen gas will burn in oxygen to produce -29458kJ of heat.