1. Tardigrade
  2. Question
  3. Chemistry
  4. 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

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

NTA AbhyasNTA Abhyas 2022

Solution:

$C_{8}H_{18}\left(\right.g\left.\right)+\frac{25}{2}O_{2}\left(\right.g\left.\right) \rightarrow 8CO_{2}\left(\right.g\left.\right)+9H_{2}O\left(\right.l\left.\right)$
$\Delta H^\circ =8\times \left(\right.-394\left.\right)+9\times \left(- 286\right)-\left(\right.-250\left.\right)$ $=-5476$