Properties of...

Properties of Enthalpy

Trending Questions

Q. Bond dissociation energy of

C H_{4} is 360 k J m o l^{- 1}

and

C_{2} H_{6} is 620 k J m o l^{- 1}

. Then bond dissociation energy of

C - C

bond is

170 kJ/mol
50 kJ /mol
80 kJ/mol
220 kJ/mol

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

the initial and the final enthalpy changes of the reaction
the state of the reactants and the products
the different intermediate reactions
the nature of the reactants and the products

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Q. During isothermal expansion of an ideal gas, its

Internal energy increases
Enthalpy decreases
Enthalpy remains unaffected
Enthalpy reduces to zero

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The enthalpy of atomisation for the reaction $C H_{4} (g) \to C (g) + 4 H (g) is 1665 k J m o l^{- 1}$ . What is the bond energy of C—H bond?

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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 _____

k J m o l^{- 1}

.
(Rounded-off to the nearest integer)

[

R = 8.314 J m o l^{- 1} K^{- 1}

]

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Q. Under which of the following conditions is the relation,

Δ H = Δ U + P Δ V

valid for a closed system.

At constant temperature
At constant volume and pressure
At constant volume
At constant pressure

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Q. Based on the values of bond energies

(B . E .)

given,

Δ_{f} H^{\circ}

N_{2} H_{4} (g)

is:
Given :

N - N = 159 {kJ mol}^{- 1}; H - H = 436 {kJ mol}^{- 1} N \equiv N = 941 {kJ mol}^{- 1}; N - H = 398 {kJ mol}^{- 1}

$711 {kJ mol}^{- 1}$
$62 {kJ mol}^{- 1}$
$- 98 {kJ mol}^{- 1}$
$- 711 {kJ mol}^{- 1}$

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What is the bond energy of covalent $O - H$ bond in water?

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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

| Δ H_{r e a c t i o n} |

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} (g)} = 35 J m o l^{- 1} K^{- 1}

and

R = 8.3 J m o l^{- 1} K^{- 1}

At. wt. of H = 1,

C_{V, H_{2} O (i)} = 75 J m o l^{- 1} K^{- 1},

heat capacity of

C O_{2} (g)

H_{2} O (l)

are taken as constant in this temperature range].

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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.

$1.50 k c a l / m o l$
$140.5 k c a l / m o l$
$130 k c a l / m o l$
$160.5 k c a l / m o l$

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Q. Under which of the following conditions is the relation,

Δ H = Δ U + P Δ V

valid for a closed system.

At constant pressure
At constant volume
At constant temperature
At constant volume and pressure

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36 m L

of pure water takes

100 s e c

to evaporate from a vessel and heater connected to an electric source which delivers

806 w a t t

. The

Δ H_{v a p o r i z a t i o n}

H_{2} O

$40.3 k J m o l^{- 1}$
$43.2 k J m o l^{- 1}$
$4.03 k J m o l^{- 1}$
None of these

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Q. For the reaction

C_{2} H_{6} \to C_{2} H_{4} + H_{2}

the reaction enthalpy,

Δ_{r} H

_____

k J m o l^{- 1}

.
[Round off to the Nearest Integer]
[Given : Bond enthalpies in

k J m o l^{- 1}

C - C : 347, C = C : 611;
C - H : 414, H - H : 436]

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

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Q. The heat of atomization of a compound

X Y_{3}

in gaseous state is

E k J m o l^{- 1}

. What is the bond energy of

X - Y

bond in

k J m o l^{- 1}

unit?

$E$
$3 E$
$\frac{E}{6}$
$\frac{E}{3}$

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

$w = 0$
$Δ U = 0$
$Δ H = 0$
$Δ (n R T) = 0$

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

$Δ U \neq 0$
$- W = q = n R T [1 - \frac{P_{2}}{P_{1}}]$
$Δ H \neq 0$
All are correct

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Q. What is an exothermic reaction?

A reaction in which energy is given off.
A reaction in which energy is gained.
A reaction in which energy is neither lost nor gained.
A reaction where bonds are broken.
A reaction where bonds are formed.

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

H F

$H F (g) \to H^{+} (g) + F^{-} (g)$
$H F (g) \to H (g) + F (g)$
$2 H F (g) \to H_{2} (g) + F_{2} (g)$
$H F (g) \to \frac{1}{2} H_{2} (g) + \frac{1}{2} F_{2} (g)$

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Q. Consider the thermodynamic data at

25^{o} C .

Molecule	$Δ H_{f}^{o} ( kJ/mol)$
$C O_{2} (g)$	$x$
$H_{2} O (l)$	$y$
$C H_{4} (g)$	$z$

The heat of combustion of

C H_{4} (g)

kJ/mol

$x + 2 y + z$
$- x + 2 y - 2 z$
$x + y - z$
$x + 2 y - z$

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Q. Enthalpy of sublimation of iodine is

24 c a l g^{- 1} a t 200^{0} C

. If specific heat

I_{2} (s) a n d I_{2} (v a p)

are

0.055 a n d 0.031 c a l g^{- 1} K^{- 1}

respectively, then enthalpy of sublimation of iodine

250^{0} C i n c a l g^{- 1}

is :

2.85
5.7
22.8
11.4

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Q. The value of standard enthalpy of formation of

S F_{6} (g), S (g) a n d F (g) a r e - 1100, 275, 80 k J / m o l

respectively. The average bond energy of

S F_{6}

(in kJ/mol) is
(Give your answer upto two decimal points)

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Q. Explain endothermic reaction with examples.

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

$Δ U \neq 0, Δ S_{t o t a l} \neq 0$
$Δ U = 0, Δ S_{t o t a l} \neq 0$
$Δ U \neq 0, Δ S_{t o t a l} = 0$
$Δ U = 0, Δ S_{t o t a l} = 0$

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

$C H_{4} (g) + O_{2} (g) M n^{2 +} - -- \to H C O O H (l) + H_{2} (g)$

$- R T$
$R T$
$- 2 R T$
$- 3 R T$

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

Amount of the reactant taken
Physical state of the reactant
Size of vessel
$Δ H$ of reaction

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Q. Latent heat of vaporisation of water is

540 c a l g^{- 1}

100^{o} C

. Calculate the entropy change when

1000 g

water is converted to steam at

100^{o} C

$1447 c a l$
$3447 c a l$
$2447 c a l$
$4447 c a l$

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Q. The bond dissociation energies of

X_{2}, Y_{2}

and

X Y

are in the ratio of

1 : 0.5 : 1

Δ H

for the formation of

X Y

- 200 k J {mol}^{- 1}

. The bond dissociation energy of

X_{2}

will be:

$800 k J {mol}^{- 1}$
$200 k J {mol}^{- 1}$
$400 k J {mol}^{- 1}$
$100 k J {mol}^{- 1}$

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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?

$T_{1} = T_{2}$
$T_{3} > T_{1}$
W $_{i s o t h e r m a l} >$ W $_{a d i a b a t i c}$
$Δ U_{i s o t h e r m a l} > Δ U_{a d i a b a t i c}$

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Q. The bond dissociation energies of

X_{2}, Y_{2}

and

X Y

are in the ratio of

1 : 0.5 : 1

Δ H

for the formation of

X Y

- 200 {kJ mol}^{- 1}

. The bond dissociation energy of

X_{2}

will be:

$200 {kJ mol}^{- 1}$
$100 {kJ mol}^{- 1}$
$800 {kJ mol}^{- 1}$
$400 {kJ mol}^{- 1}$

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