Draw an enthalpy cycle to calculate the enthalpy change of formation of ethanol, ${\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH}$, using enthalpy changes of combustion.

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?

When red phosphorus burns in oxygen the enthalpy change is $-2967 \mathrm{kJ} {\mathrm{mol}}^{-1}$. For white phosphorus the enthalpy change is $-2984 \mathrm{kJ} {\mathrm{mol}}^{-1}$. For both forms of phosphorus the reaction taking place is: ${\mathrm{P}}_4\left(\mathrm{s}\right)+5{\mathrm{O}}_2\left(\mathrm{g}\right)\to {\mathrm{P}}_4{\mathrm{O}}_{10}\left(\mathrm{s}\right)$.

Use this information to calculate the enthalpy change for the transformation: ${\mathrm{P}}_4\left(\mathrm{white}\right)\to {\mathrm{P}}_4\left(\mathrm{red}\right)$.