S C Kheterpal, S N Dhawan and, P N Kapil Solutions for Chapter: Thermodynamics, Exercise 5: PROBLEMS FOR PRACTICE

Ethylene on combustion gives carbon dioxide and water. Its enthalpy of combustion is $141.0 \mathrm{kJ} {\mathrm{mol}}^{-1}$. If the enthalpy of formation of ${\mathrm{CO}}_2$ and ${\mathrm{H}}_2\mathrm{O}$ are $393.3 \mathrm{kJ}$ and $286.2 \mathrm{kJ}$ respectively. Calculate the enthalpy of formation of ethylene.

Calculate the enthalpy of formation of carbon disulphide. Given that the enthalpy of combustion of carbon disulphide is $110.2 \mathrm{kJ} {\mathrm{mol}}^{-1}$and those of sulphur and carbon are $297.4 \mathrm{kJ}/\mathrm{g}$ atom and $394.5 \mathrm{kJ}/\mathrm{g}$ atom respectively.

Calculate the enthalpy of formation of sucrose $\left({\mathrm{C}}_{12}{\mathrm{H}}_{22}{\mathrm{O}}_{11}\right)$ from the following data :-

${\mathrm{C}}_{12}{\mathrm{H}}_{22}{\mathrm{O}}_{11}+12{\mathrm{O}}_2\to 12{\mathrm{CO}}_2+11{\mathrm{H}}_2\mathrm{O}$, $\mathrm{\Delta H}=–5200.7 \mathrm{kJ} {\mathrm{mol}}^{-1}$.

$\mathrm{C}+{\mathrm{O}}_2\to {\mathrm{CO}}_2, \mathrm{\Delta H}=–394.5 \mathrm{kJ} {\mathrm{mol}}^{-1}$.

${\mathrm{H}}_2+\frac{1}{2}{\mathrm{O}}_2\to {\mathrm{H}}_2\mathrm{O}, \mathrm{\Delta H}=–285.8 \mathrm{kJ} {\mathrm{mol}}^{-1}$.

Calculate the standard enthalpy of formation of ${\mathrm{SO}}_3$ at $298 \mathrm{K}$ using the following reactions and enthalpies.

${\mathrm{S}}_8\left(\mathrm{s}\right)+8{\mathrm{O}}_2\left(\mathrm{g}\right)\to 8{\mathrm{SO}}_2\left(\mathrm{g}\right), {\mathrm{H}}^{\mathrm{o}}=-2775 \mathrm{kJ} {\mathrm{mol}}^{-1}$.

$2{\mathrm{SO}}_2\left(\mathrm{g}\right)+{\mathrm{O}}_2\left(\mathrm{g}\right)\to 2{\mathrm{SO}}_3\left(\mathrm{g}\right), {\mathrm{H}}^{\mathrm{o}}=-198 \mathrm{kJ} {\mathrm{mol}}^{-1}$.

Calculate the enthalpy of formation of anhydrous ${\mathrm{Al}}_2{\mathrm{Cl}}_6$ from the following data:

$$\begin{gathered} \left(\mathrm{i}\right) 2\mathrm{Al}\left(\mathrm{s}\right)+6\mathrm{HCl}\left(\mathrm{aq}\right)\to {\mathrm{Al}}_2{\mathrm{Cl}}_6\left(\mathrm{aq}\right)+3{\mathrm{H}}_2\left(\mathrm{g}\right) +1004.2 \mathrm{kJ} {\mathrm{mol}}^{-1}. \\ \left(\mathrm{ii}\right) {\mathrm{H}}_2\left(\mathrm{g}\right) +{\mathrm{Cl}}_2\left(\mathrm{g}\right)\to 2\mathrm{HCl}\left(\mathrm{g}\right) +184 \mathrm{kJ} {\mathrm{mol}}^{-1}. \\ \left(\mathrm{iii}\right) \mathrm{HCl}\left(\mathrm{g}\right)+ \mathrm{aq}\to \mathrm{HCl}\left(\mathrm{aq}\right) +73.2 \mathrm{kJ} {\mathrm{mol}}^{-1}. \\ \left(\mathrm{iv}\right) {\mathrm{Al}}_2{\mathrm{Cl}}_6\left(\mathrm{s}\right)+ \mathrm{aq}\to {\mathrm{Al}}_2{\mathrm{Cl}}_6\left(\mathrm{aq}\right) 643.1 \mathrm{kJ} {\mathrm{mol}}^{-1}. \end{gathered}$$

From the following thermochemical equations, calculate the standard enthalpy of formation of $\mathrm{HCl} \left(\mathrm{g}\right)$.

$$\begin{gathered} \left(\mathrm{A}\right) {\mathrm{H}}_2\left(\mathrm{g}\right) \to 2\mathrm{H}\left(\mathrm{g}\right), ∆\mathrm{H}°=+436.0 \mathrm{kJ} {\mathrm{mol}}^{-1}. \\ \left(\mathrm{B}\right) {\mathrm{Cl}}_2\left(\mathrm{g}\right) \to 2\mathrm{Cl}\left(\mathrm{g}\right), ∆\mathrm{H}°=+242.7 \mathrm{kJ} {\mathrm{mol}}^{-1}. \\ \left(\mathrm{C}\right) \mathrm{HCl}\left(\mathrm{g}\right) \to \mathrm{H}\left(\mathrm{g}\right) + \mathrm{Cl}\left(\mathrm{g}\right), ∆\mathrm{H}°=+431.8 \mathrm{kJ} {\mathrm{mol}}^{-1}. \end{gathered}$$

Calculate the enthalpy of formation of acetic acid if the enthalpy of combustion to ${\mathrm{CO}}_2\left(\mathrm{g}\right)$ and ${\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)$ is $- 867.0 \mathrm{kJ} {\mathrm{mol}}^{-1}$and enthalpies of formation of ${\mathrm{CO}}_2\left(\mathrm{g}\right)$ and ${\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)$ are respectively $- 393.5$ and $- 285.9 \mathrm{kJ} {\mathrm{mol}}^{-1}$•

The enthalpy of combustion of ethyl alcohol (${\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH}$) is $1380.7 \mathrm{kJ} {\mathrm{mol}}^{-1}$. If the enthalpies of formation of ${\mathrm{CO}}_2$ and ${\mathrm{H}}_2\mathrm{O}$ are $394.5$ and $286.6 \mathrm{kJ} {\mathrm{mol}}^{-1}$ respectively. Calculate the enthalpy of formation of ethyl alcohol.