The standard enthalpy of formation of octane (.C8H18.) is - 250 textkJmol- 1 . The enthalpy of formation of CO2(.g.) and H2O(.l.) are - 394 textkJmol- 1 and - 286 textkJmol- 1 respectively. The enthalpy of combustion of C8H18(.g.) is

Question

The standard enthalpy of formation of octane (.C8H18.) is - 250 textkJmol- 1 . The enthalpy of formation of CO2(.g.) and H2O(.l.) are - 394 textkJmol- 1 and - 286 textkJmol- 1 respectively. The enthalpy of combustion of C8H18(.g.) is (A) - 5200 textkJmol- 1 (B) - 5726 textkJmol- 1 (C) - 5476 textkJmol- 1 (D) - 5310 textkJmol- 1

Tardigrade Admin · Accepted Answer

C8H18(.g.)+(25/2)O2(.g.) arrow 8CO2(.g.)+9H2O(.l.) Δ H° =8× (.-394.)+9× (- 286)-(.-250.) =-5476

Q. The standard enthalpy of formation of octane $(C_{8} H_{18})$ is $- 250 kJmol^{- 1}$ . The enthalpy of formation of $C O_{2} (g)$ and $H_{2} O (l)$ are $- 394 kJmol^{- 1}$ and $- 286 kJmol^{- 1}$ respectively. The enthalpy of combustion of $C_{8} H_{18} (g)$ is

$- 5200 kJmol^{- 1}$

$- 5726 kJmol^{- 1}$

$- 5476 kJmol^{- 1}$

$- 5310 kJmol^{- 1}$

$C_{8} H_{18} (g) + \frac{25}{2} O_{2} (g) \to 8 C O_{2} (g) + 9 H_{2} O (l)$
$Δ H^{\circ} = 8 \times (- 394) + 9 \times (- 286) - (- 250)$ $= - 5476$

Q. The standard enthalpy of formation of octane (C8​H18​) is −250kJmol−1 . The enthalpy of formation of CO2​(g) and H2​O(l) are −394kJmol−1 and −286kJmol−1 respectively. The enthalpy of combustion of C8​H18​(g) is

−5200kJmol−1

−5726kJmol−1

−5476kJmol−1

−5310kJmol−1