Embibe Experts Solutions for Chapter: Thermodynamics & Thermochemistry, Exercise 2: KVPY PROBLEMS (PREVIOUS YEARS)

The molar enthalpy change for ${\mathrm{H}}_2\mathrm{O} \left(\mathrm{l}\right)\rightleftharpoons \mathrm{H}2\mathrm{O} \left(\mathrm{g}\right)$ at $373 \mathrm{K}$ and $1 \mathrm{atm}$ is $41 \mathrm{kJ}/\mathrm{mol}$. Assuming ideal behaviour, the internal energy change for vaporisation of $1 \mathrm{mol}$ of water at $373 \mathrm{K}$ and $1 \mathrm{atm}$ in $\mathrm{kJ} {\mathrm{mol}}^{-1}$ is:

Given that the bond energies of: $\mathrm{N}\equiv \mathrm{N}$ is $946 \mathrm{kJ} {\mathrm{mol}}^{-1}, \mathrm{H}-\mathrm{H}$ is $435 \mathrm{kJ} {\mathrm{mol}}^{-1}, \mathrm{N}-\mathrm{N}$ is $159 \mathrm{kJ} {\mathrm{mol}}^{-1}$, and $\mathrm{N}-\mathrm{H}$ is $389 \mathrm{kJ} {\mathrm{mol}}^{-1}$, the heat of formation of hydrazine in the gas phase in $\mathrm{kJ} {\mathrm{mol}}^{-1}$ is:

The standard free energy change (in $\mathrm{J}$) for the reaction $3{\mathrm{Fe}}^{2+ }\left(\mathrm{aqeous}\right)+2\mathrm{Cr} \left(\mathrm{s}\right)\to 2{\mathrm{Cr}}^{3+ }\left(\mathrm{aqeous}\right)+3\mathrm{Fe} \left(\mathrm{s}\right)$ given ${\mathrm{E}}_{{\mathrm{Fe}}^{2+}/\mathrm{Fe}}^0=-0.44 \mathrm{V}$ and ${\mathrm{E}}_{{\mathrm{Cr}}^{3+}/\mathrm{Cr}}^0=-0.74 \mathrm{V}$ is $\left(\mathrm{F}=96500 \mathrm{C}\right)$.

For the reaction ${\mathrm{N}}_2+3{\mathrm{X}}_2\to 2{\mathrm{NX}}_3$ where $\mathrm{X}=\mathrm{F}, \mathrm{Cl}$ (the average bond energies are $\mathrm{F}-\mathrm{F}=155 \mathrm{kJ} {\mathrm{mol}}^{-1}, \mathrm{N}-\mathrm{F}=272 \mathrm{kJ} {\mathrm{mol}}^{-1}, \mathrm{Cl}-\mathrm{Cl}=242 \mathrm{kJ} {\mathrm{mol}}^{-1}, \mathrm{N}-\mathrm{Cl}=200 \mathrm{kJ} {\mathrm{mol}}^{-1}$ and $\mathrm{N}\equiv \mathrm{N}=941 \mathrm{kJ} {\mathrm{mol}}^{-1}$). The heats of the formation of ${\mathrm{NF}}_3$ and ${\mathrm{NCl}}_3$ in $\mathrm{kJ} {\mathrm{mol}}^{-1}$, respectively, are closest to:

Given:

$\mathrm{NO} \left(\mathrm{g}\right)+{\mathrm{O}}_{3 }\left(\mathrm{g}\right)⟶{\mathrm{NO}}_2 \left(\mathrm{g}\right)+{\mathrm{O}}_2 \left(\mathrm{g}\right) \mathrm{\Delta H}=-198.9 \mathrm{kJ}/\mathrm{mol}$

${\mathrm{O}}_{3 }\left(\mathrm{g}\right)⟶3/2{\mathrm{O}}_{2 }\left(\mathrm{g}\right) \mathrm{\Delta H}=-142.3 \mathrm{kJ}/\mathrm{mol}$

${\mathrm{O}}_2 \left(\mathrm{g}\right)⟶2\mathrm{O} \left(\mathrm{g}\right) \mathrm{\Delta H}=+495.0 \mathrm{kJ}/\mathrm{mol}$

The enthalpy change $\left(∆\mathrm{H}\right)$ for the following reaction is:

$\mathrm{NO} \left(\mathrm{g}\right)+\mathrm{O} \left(\mathrm{g}\right)⟶{\mathrm{NO}}_2 \left(\mathrm{g}\right)$

A system consisting of $1 \mathrm{mol}$ of an ideal gas undergoes a reversible process, $\mathrm{A}\to \mathrm{B}\to \mathrm{C}\to \mathrm{A}$ (schematically indicated in the figure below). If the temperature at the starting point $\mathrm{A}$ is $300 \mathrm{K}$ and the work done in the process $\mathrm{B}\to \mathrm{C}$ is $1 \mathrm{L} \mathrm{atm}$, the heat exchanged in the entire process in $\mathrm{L} \mathrm{atm}$ is:

Nitroglycerin (Molecular weight $=227.1$) detonates according to the following equation:

$2{\mathrm{C}}_3{\mathrm{H}}_5{\left({\mathrm{NO}}_3\right)}_3\left(\mathrm{l}\right)\to 3 {\mathrm{N}}_2\left(\mathrm{g}\right)+\frac{1}{2}{\mathrm{O}}_2\left(\mathrm{g}\right)+6{\mathrm{CO}}_2\left(\mathrm{g}\right)+5{\mathrm{H}}_2\mathrm{O}\left(\mathrm{g}\right)$

The standard molar enthalpies of formation, ${\mathrm{\Delta H}}_{\mathrm{f}}^0$, for the compounds are given below:

${\mathrm{\Delta H}}_{\mathrm{f}}^0\left[{\mathrm{C}}_3{\mathrm{H}}_5{\left({\mathrm{NO}}_3\right)}_3\right]=-364 \mathrm{kJ}/\mathrm{mol}; {\mathrm{\Delta H}}_{\mathrm{f}}^0\left[{\mathrm{CO}}_2\left(\mathrm{g}\right)\right]=-393.5 \mathrm{kJ}/\mathrm{mol}$.

${\mathrm{\Delta H}}_{\mathrm{f}}^2\left[{\mathrm{H}}_2\mathrm{O}\left(\mathrm{g}\right)\right]=-241.8 \mathrm{kJ}/\mathrm{mol}; {\mathrm{\Delta H}}_{\mathrm{f}}^0\left[{\mathrm{N}}_2\left(\mathrm{g}\right)\right]=0 \mathrm{kJ}/\mathrm{mol}; {\mathrm{\Delta H}}_{\mathrm{f}}^0\left[{\mathrm{O}}_2\left(\mathrm{g}\right)\right]=0 \mathrm{kJ}/\mathrm{mol}$.

The enthalpy change when $10 \mathrm{g}$ nitroglycerine is detonated is:

The quantity of heat (in $\mathrm{J}$) required to raise the temperature of $1.0 \mathrm{kg}$ of ethanol from $293.45 \mathrm{K}$ to the boiling point and then change the liquid to vapor at that temperature is closest to [Given: Boiling point of ethanol $351.45 \mathrm{K}$]

Specific heat capacity of liquid ethanol $2.44 \mathrm{J} {\mathrm{g}}^{-1} {\mathrm{K}}^{-1}$.

Latent heat of vaporization of ethanol $855 \mathrm{J} {\mathrm{g}}^{-1}$].