1. Tardigrade
  2. Question
  3. Chemistry
  4. The heat of formation of methane at 25° C at a constant pressure is -17.890 kcal. Its heat of formation at constant volume is: [R=1.987 kcal degree -1 mol -1 ]

Question Error Report

Thank you for reporting, we will resolve it shortly

Back to Question

Q. The heat of formation of methane at $25^{\circ} C$ at a constant pressure is $-17.890$ kcal. Its heat of formation at constant volume is : $[R=1.987$ kcal degree $^{-1}\, mol ^{-1}$ ]

BHUBHU 2002

Solution:

Write the equation for heat of formation of $CH _{4}$ first to calculate $n_{g}$ then calculate $\Delta E$ Cheat of formation of $CH _{4}$ at constant volume) by using formula
$\Delta E=\Delta H+\Delta n_{g} R T$
$\Delta H=-17.890$ kcal
Given,
$R =1.987 \text { kcal degree }^{-1} \,mol ^{-1} $
$T =25^{\circ} C =25+273=298 \,K$
$C (s)+2 H _{2}(g) \longrightarrow CH _{4}( g ) $
$\Delta n_{g}=$ number of moles of gaseous products $-$ number of moles of gaseous reactants
$=1-2=-1 $
$\Delta E =\Delta H-n R T$
$=-17.890+\left(-1 \times 1.987 \times 10^{3} \times 298\right)$
$=-17.297$ kcal