Properties of Enthalpy

Q. Bond dissociation energy of $C{H}_4\text{is}360kJmo{l}^{-1}$ and $C_2{H}_6\text{is}620kJmo{l}^{-1}$. Then bond dissociation energy of $C-C$ bond is

1. 170 kJ/mol
2. 50 kJ /mol
3. 80 kJ/mol
4. 220 kJ/mol

Q. The enthalpy change of a reaction does not depend on:

1. the initial and the final enthalpy changes of the reaction
2. the state of the reactants and the products
3. the different intermediate reactions
4. the nature of the reactants and the products

Q. During isothermal expansion of an ideal gas, its

1. Internal energy increases
2. Enthalpy decreases
3. Enthalpy remains unaffected
4. Enthalpy reduces to zero

Q.

The enthalpy of atomisation for the reaction $C{H}_4\left(g\right)\to C\left(g\right)+4H\left(g\right)\text{is}1665kJmo{l}^{-1}$. What is the bond energy of C—H bond?

Q. Five moles of an ideal gas at 293 K is expanded isothermally from an initial pressure of 2.1 MPa to 1.3 MPa against at constant external pressure 4.3 MPa. The heat transferred in this process is _____ $kJmo{l}^{-1}$.
(Rounded-off to the nearest integer)

[$R=8.314Jmo{l}^{-1}{K}^{-1}$]

Q. Under which of the following conditions is the relation,
$\Delta H=\Delta U+P\Delta V$
valid for a closed system.

1. At constant temperature
2. At constant volume and pressure
3. At constant volume
4. At constant pressure

Q. Based on the values of bond energies $(B.E.)$ given, ${\Delta }_f{H}^{\circ }$ of $N_2{H}_4\left(g\right)$ is:
Given : $N-N=159{\text{kJ mol}}^{-1};H-H=436{\text{kJ mol}}^{-1}N\equiv N=941{\text{kJ mol}}^{-1};N-H=398{\text{kJ mol}}^{-1}$

1. $711{\text{kJ mol}}^{-1}$
2. $62{\text{kJ mol}}^{-1}$
3. $-98{\text{kJ mol}}^{-1}$
4. $-711{\text{kJ mol}}^{-1}$

Q.

What is the bond energy of covalent $\mathrm{O}-\mathrm{H}$ bond in water?

Q. A pellet of naphthalene of mass 1.28 g is burnt in a bomb calorimeter with heat capacity 14000 J/K. If the initial temperature is 300K and final temperature is 302K.
The $|\Delta H_{reaction}|$ for 1 mole of napthalene at 300 K in KJ/mole (consider reactant & products at 300K).
[At. wt. of C = 12, $C_{V,C{O}_2\left(g\right)}=35Jmo{l}^{-1}{K}^{-1}$ and $R=8.3Jmo{l}^{-1}{K}^{-1}$
At. wt. of H = 1, $C_{V,H_{2}O\left(i\right)}=75Jmo{l}^{-1}{K}^{-1},$ heat capacity of $C{O}_2\left(g\right)$ & $H_{2}O\left(l\right)$ are taken as constant in this temperature range].

Q. The heat of formation of ethylene is 12.5 kcal. Calculate C=C bond energy in ethylene from the following data. Heat of atomisation of C=170.1 kcal/mole, heat of atomisation of H=52.1 kcal/mole, bond energy of C-H=99.3 kcal/mole.

1. $1.50kcal/mol$
2. $140.5kcal/mol$
3. $130kcal/mol$
4. $160.5kcal/mol$

Q. Under which of the following conditions is the relation,
$\Delta H=\Delta U+P\Delta V$
valid for a closed system.

1. At constant pressure
2. At constant volume
3. At constant temperature
4. At constant volume and pressure

Q. $36mL$ of pure water takes $100sec$ to evaporate from a vessel and heater connected to an electric source which delivers $806watt$. The $\Delta H_{vaporization}$ of $H_{2}O$ is

1. $40.3kJmo{l}^{-1}$
2. $43.2kJmo{l}^{-1}$
3. $4.03kJmo{l}^{-1}$
4. None of these

Q. For the reaction
$C_2{H}_6\to C_2{H}_4+H_2$
the reaction enthalpy, ${\Delta }_{r}H$ _____$kJmo{l}^{-1}$.
[Round off to the Nearest Integer]
[Given : Bond enthalpies in $kJmo{l}^{-1}$
C - C : 347, C = C : 611;
C - H : 414, H - H : 436]

Q.

The properties of water are ___________ from that of oxygen and hydrogen.

Q. The heat of atomization of a compound $X{Y}_3$ in gaseous state is $EkJmo{l}^{-1}$. What is the bond energy of $X-Y$ bond in $kJmo{l}^{-1}$ unit?

1. $E$
2. $3E$
3. $\frac{E}{6}$
4. $\frac{E}{3}$

Q. Which is/are true about isothermal process of an ideal gas.

1. $w=0$
2. $\Delta U=0$
3. $\Delta H=0$
4. $\Delta \left(nRT\right)=0$

Q. In an isothermal irreversible expansion of an ideal gas:

1. $\Delta U\ne 0$
2. $-W=q=nRT[1-\frac{P_2}{P_1}]$
3. $\Delta H\ne 0$
4. All are correct

Q. What is an exothermic reaction?

1. A reaction in which energy is given off.
2. A reaction in which energy is gained.
3. A reaction in which energy is neither lost nor gained.
4. A reaction where bonds are broken.
5. A reaction where bonds are formed.

Q. Among the following, for which reaction heat of reaction also represents the bond energy of $HF$?

1. $HF\text{(g)}\to H^{+}\text{(g)}+F^{-}\text{(g)}$
2. $HF\text{(g)}\to H\text{(g)}+F\text{(g)}$
3. $2HF\text{(g)}\to H_2\text{(g)}+F_2\text{(g)}$
4. $HF\text{(g)}\to \frac{1}{2}{H}_2\text{(g)}+\frac{1}{2}{F}_2\text{(g)}$

Q. Consider the thermodynamic data at ${25}^{o}C.$

Molecule	$\Delta H_f^o\text{( kJ/mol)}$
$C{O}_2\left(g\right)$	$x$
$H_{2}O\left(l\right)$	$y$
$C{H}_4\left(g\right)$	$z$

The heat of combustion of $C{H}_4\left(g\right)$ in $\text{kJ/mol}$is

1. $x+2y+z$
2. $-x+2y-2z$
3. $x+y-z$
4. $x+2y-z$

Q. Enthalpy of sublimation of iodine is $24cal{g}^{-1}at{200}^{0}C$. If specific heat $I_2\left(s\right)and{I}_2\left(vap\right)$ are$0.055and0.031cal{g}^{-1}{K}^{-1}$ respectively, then enthalpy of sublimation of iodine ${250}^{0}Cincal{g}^{-1}$ is :

1. 2.85
2. 5.7
3. 22.8
4. 11.4

Q. The value of standard enthalpy of formation of $S{F}_6\left(g\right),S\left(g\right)andF\left(g\right)are-1100,275,80kJ/mol$ respectively. The average bond energy of $S{F}_6$ (in kJ/mol) is
(Give your answer upto two decimal points)

Q. Explain endothermic reaction with examples.

Q.

The difference in the heat of reaction at constant volume and at constant pressure for the given reaction is:

$C{H}_4\left(g\right)+O_2\left(g\right)\stackrel{M{n}^{2+}}{\to }HCOOH\left(l\right)+H_2\left(g\right)$

1. $–RT$
2. $RT$
3. $-2RT$
4. $–3RT$

Q. For irreversible expansion of an ideal gas under isothermal condition, the correct option is :

1. $\Delta U\ne 0,\Delta S_{total}\ne 0$

2. $\Delta U=0,\Delta S_{total}\ne 0$

3. $\Delta U\ne 0,\Delta S_{total}=0$

4. $\Delta U=0,\Delta S_{total}=0$

Q. Which of the following does not affect the rate of reaction?

1. Amount of the reactant taken
2. Physical state of the reactant
3. Size of vessel
4. $\Delta H$ of reaction

Q. Latent heat of vaporisation of water is $540cal{g}^{-1}$ at ${100}^{o}C$. Calculate the entropy change when $1000g$ water is converted to steam at ${100}^{o}C$.

1. $1447cal$
2. $3447cal$
3. $2447cal$
4. $4447cal$

Q. The bond dissociation energies of $X_2,Y_2$ and $XY$ are in the ratio of $1:0.5:1$
$\Delta H$ for the formation of $XY$ is$-200kJ{\text{mol}}^{-1}$. The bond dissociation energy of $X_2$ will be:

1. $800kJ{\text{mol}}^{-1}$
2. $200kJ{\text{mol}}^{-1}$
3. $400kJ{\text{mol}}^{-1}$
4. $100kJ{\text{mol}}^{-1}$

Q. The reversible expansion of an ideal gas under adiabatic and isothermal conditions is shown in the figure. Which of the following statement(s) is(are) correct?

1. $T_1=T_2$
2. $T_3>T_1$
3. W${}_{isothermal}>$W${}_{adiabatic}$
4. $\Delta U_{isothermal}>\Delta U_{adiabatic}$

Q. The dissociation energy of methane is $360kcalmo{l}^{-1}$. The average bond energy of $C--H$ bond in $kcalmo{l}^{-1}$ is ______.