A student added $50 {\mathrm{cm}}^3$ of sodium hydroxide to $50 {\mathrm{cm}}^3$ of hydrochloric acid. Both solutions were at $18 °\mathrm{C}$ to start with. When the solutions were mixed a reaction occurred. The temperature rose to $33 °\mathrm{C}$. How much energy is released in this reaction?

A student added $10 \mathrm{g} (0.25 \mathrm{mol})$ of sodium hydroxide to $40 {\mathrm{cm}}^3$ of water to make a concentrated solution. All the sodium hydroxide dissolved. The student measured the maximum temperature rise. The student suggested that these results would give an accurate value for the standard enthalpy change of solution. Give two reasons why the student is incorrect.

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?