A student calculated the standard enthalpy change of combustion of ethanol $∆{\mathrm{H}}_{\mathrm{c}}^{°}\left[{\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH}\right]$ by calorimetry as $- 870 \mathrm{kJ} {\mathrm{mol}}^{-1}$. The data book value is $-1367 \mathrm{kJ} {\mathrm{mol}}^{-1}$. Explain why there is a difference between these values.

Calculate $∆{\mathrm{H}}_{\mathrm{r}}^{°}$ using the following information,

$$\begin{gathered} ∆{\mathrm{H}}_{\mathrm{f}}^{°}\left[{\mathrm{Fe}}_2{\mathrm{O}}_3\left(\mathrm{s}\right)\right]=-824.2 \mathrm{kJ} {\mathrm{mol}}^{-1}. \\ ∆{\mathrm{H}}_{\mathrm{f}}^{°}\left[{\mathrm{Al}}_2{\mathrm{O}}_3\left(\mathrm{s}\right)\right]=-1675.7 \mathrm{kJ} {\mathrm{mol}}^{-1}. \end{gathered}$$

Calculate a value for $∆{\mathrm{H}}_{\mathrm{f}}^{°}\left[{\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH}\left(\mathrm{l}\right)\right]$ using the following data:

$$\begin{gathered} ∆{\mathrm{H}}_{\mathrm{c}}^{°}\left[\mathrm{C}\left(\mathrm{graphite}\right)\right]=-393.5 \mathrm{kJ} {\mathrm{mol}}^{-1}. \\ ∆{\mathrm{H}}_{\mathrm{c}}^{°}\left[{\mathrm{H}}_2\left(\mathrm{g}\right)\right]=-285.8 \mathrm{kJ} {\mathrm{mol}}^{-1}. \\ ∆{\mathrm{H}}_{\mathrm{c}}^{°}\left[{\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH}\left(\mathrm{l}\right)\right]=-1367.3 \mathrm{kJ} {\mathrm{mol}}^{-1}. \end{gathered}$$

Look at this equation.

$3\mathrm{Mg}\left(\mathrm{s}\right)+{\mathrm{Fe}}_2{\mathrm{O}}_3\left(\mathrm{s}\right)\to 2\mathrm{Fe}\left(\mathrm{s}\right)+3\mathrm{MgO}\left(\mathrm{s}\right)$.

Which one of the following gives the correct value for the enthalpy change of this reaction?

Use the information in Figure and the information below to demonstrate that the average bond energy of the $\mathrm{C}-\mathrm{H}$ bond is $415.9 \mathrm{kJ} {\mathrm{mol}}^{-1}$.

$$\begin{gathered} ∆{\mathrm{H}}_{\mathrm{f}}^{°}\left[{\mathrm{CH}}_4\right]=-74.8 \mathrm{kJ} {\mathrm{mol}}^{-1}. \\ ∆{\mathrm{H}}_{\mathrm{at}}^{°}\left[\frac{1}{2}\mathrm{H}\right]=+218 \mathrm{kJ} {\mathrm{mol}}^{-1}. \\ ∆{\mathrm{H}}_{\mathrm{at}}^{°}\left[\mathrm{C}\left(\mathrm{graphite}\right)\right]=+716.7 \mathrm{kJ} {\mathrm{mol}}^{-1}. \end{gathered}$$

Look at this equation.

${\mathrm{CH}}_4\left(\mathrm{g}\right)+2{\mathrm{O}}_2\left(\mathrm{g}\right)\to {\mathrm{CO}}_2\left(\mathrm{g}\right)+2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{g}\right)$.

Which one of the following statements is completely correct?