The standard enthalpies of formation of H2O(l) and CO2(g) are respectively -286 kJ mol-1 and -394 kJ mol-1. If the standard heat of combustion of CH4(g) is -891 kJ mol-1, then the standard enthalpy of formation of CH4(g) is

Question

The standard enthalpies of formation of H2O(l) and CO2(g) are respectively -286 kJ mol-1 and -394 kJ mol-1. If the standard heat of combustion of CH4(g) is -891 kJ mol-1, then the standard enthalpy of formation of CH4(g) is (A) -75 kJ mol-1 (B) +75 kJ mol-1 (C) -211 kJ mol-1 (D) +211 kJ mol-1

Tardigrade Admin · Accepted Answer

H 2+(1/2) O 2 arrow H 2 O , Δf H 0=-286 C + O 2 arrow CO 2, Δf H 0=-394 CH 4+2 O 2 arrow CO 2+2 H 2 O , Δ C H 0-891 C +2 H 2 arrow CH 4 Δf H =? -394+(-286 × 2)+891=-75 kJ mol -1

Q. The standard enthalpies of formation of $H_{2} O (l)$ and $C O_{2} (g)$ are respectively $- 286 k J m o l^{- 1}$ and $- 394 k J m o l^{- 1}$ . If the standard heat of combustion of $C H_{4} (g)$ is $- 891 k J m o l^{- 1}$ , then the standard enthalpy of formation of $C H_{4} (g)$ is

$- 75 k J m o l^{- 1}$

$+ 75 k J m o l^{- 1}$

$- 211 k J m o l^{- 1}$

$+ 211 k J m o l^{- 1}$

$- 1571 k J m o l^{- 1}$

$H_{2} + \frac{1}{2} O_{2} \to H_{2} O, Δ_{f} H^{0} = - 286$
$C + O_{2} \to C O_{2}, Δ_{f} H^{0} = - 394$
$C H_{4} + 2 O_{2} \to C O_{2} + 2 H_{2} O, Δ_{C} H^{0} - 891$
$C + 2 H_{2} \to C H_{4} Δ_{f} H = ?$
$- 394 + (- 286 \times 2) + 891 = - 75 k J m o l^{- 1}$

Q. The standard enthalpies of formation of H2​O(l) and CO2​(g) are respectively −286kJmol−1 and −394kJmol−1. If the standard heat of combustion of CH4​(g) is −891kJmol−1, then the standard enthalpy of formation of CH4​(g) is

−75kJmol−1

+75kJmol−1

−211kJmol−1

+211kJmol−1

−1571kJmol−1

H2​+21​O2​→H2​O,Δf​H0=−286 C+O2​→CO2​,Δf​H0=−394 CH4​+2O2​→CO2​+2H2​O,ΔC​H0−891 C+2H2​→CH4​Δf​H=? −394+(−286×2)+891=−75kJmol−1