Enthalpy

Trending Questions

Q. Ethyl chloride

(C_{2} H_{5} C l)

is prepared by reaction of ethylene with hydrogen chloride:

C_{2} H_{4} (g) + H C l (g) \to C_{2} H_{5} C l (g) △ H = - 72.3 k J / m o l

What is the value of

△ U

(in

k J

), if

98 g

of ethylene and 109.5 g of

H C l

are allowed to react at

300 K

$- 64.81$
$- 190.71$
$- 209.41$
$- 224.38$

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Q. Consider an endothermic reaction

X \to Y

with the activation energies

E_{b}

and

E_{f}

for the backward and forward reactions respectively. Here

$E_{b} > E_{f}$
$E_{b} < E_{f}$
$E_{b} = E_{f}$
Cannot predict

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The enthalpy of combustion of 2 moles of benzene at $27^{\circ} C$ differs from the value determined by bomb calorimeter by

7.483 kJ
-7.483 kJ
2.494 kJ
-2.494 kJ

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Q. One mole of a non- ideal gas undergoes a change of state

(2.0 a t m, 3.0 L, 95 K) \to (4.0 a t m, 5.0 L, 245 K)

with a change in internal energy,

△ U = 30.0 L

atm. The change in enthalpy

(△ H)

of the process is:

$40.0 L a t m$
$42.3 L a t m$
$44.0 L a t m$
Not defined, because pressure is not constant

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Q. Choose the reaction(s) from the following options for which the standard enthalpy of reaction is equal to the standard enthalpy of formation:

$2 C (g) + 3 H_{2} (g) ⟶ C_{2} H_{6} (g)$
$\frac{3}{2} O_{2} (g) ⟶ O_{3} (g)$
$2 H_{2} (g) + O_{2} (g) ⟶ 2 H_{2} O (ℓ)$
$\frac{1}{8} S_{8} (s) + O_{2} (g) ⟶ S O_{2} (g)$

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Q. Bond dissociation enthalpy is always

Endothermic
Exothermic
Depends upon the nature of bond formed
Cannot be predicted

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Q. One mole of Helium gas undergoes a reversible cyclic process ABCDA as shown in the figure. Assuming the gas to the ideal, answer the following questions:

What is the value of

Δ H

for the overall cyclic process?

$- 100 R ln 2$
$+ 100 R ln 2$
$+ 200 R ln 2$
Zero

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Q. The difference between

C_{p}

and

C_{v}

can be derived from

H = U + P V

. Calculate the difference between

C_{p}

and

C_{v}

for 7.5 moles of an ideal gas.

$82.36$ $J m o l^{- 1} K^{- 1}$
$72.36$ $J m o l^{- 1} K^{- 1}$
$62.36$ $J m o l^{- 1} K^{- 1}$
$52.36$ $J m o l^{- 1} K^{- 1}$

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Q. One mole of a gas is expanded from (1 L, 10 atm, 300K) to (4 L, 5 atm, 600K) against a constant external pressure of 1 atm. The heat capacity of gas is

50 J / K .

Then the enthalpy change during the process is (1 L atm

≃

100 J)

$△ H = 15 k J$
$△ H = 15.7 k J$
$△ H = 14.4 k J$
$△ H = 14.7 k J$

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Q. The enthalpy of vapourisation of water from the following equations is:

H_{2} (g) + \frac{1}{2} O_{2} (g) \to H_{2} O (l), △ H = - 286 kJ

H_{2} (g) + \frac{1}{2} O_{2} (g), \to H_{2} O (g), △ H = - 245.5 kJ

$6.02 kJ$
$40.5 kJ$
$62.3 kJ$
$1.25 kJ$

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When 1 mole of oxalic acid is treated with excess of NaOH in dilute aqueous solution, 106 kJ of heat is liberated. Predict the enthalpy of ionization of the acid ?

$4.3 k J m o l^{- 1}$
$- 4.3 k J m o l^{- 1}$
$- 8.6 k J m o l^{- 1}$
$8.6 k J m o l^{- 1}$

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Q. Enthalpy of fusion of a liquid is

1.435 k c a l m o l^{- 1}

and molar entropy change is

5.26 c a l m o l^{- 1} K^{- 1}

, hence melting point of liquid is

$100^{\circ} C$
$0^{\circ} C$
$373 K$
$- 273^{\circ} C$

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Q. Two moles of an ideal gas is expanded isothermally and reversibly from 1 litre to 10 litre at 300 K. The enthalpy change ( in kJ) for the process is

11.4 kJ
−11.4 kJ
0 kJ
4.8 kJ

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Q. Enthalpy of atomisation of a diamond is

600 k J / m o l .

C (d i a m o n d) \to C (g) .

Using this data the bond energy of C-C bond was found to be

x \times 10^{2} k J / m o l

where x is an interger between 0 to 9. Value of x is

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Standard enthalpy of combustion of $C H_{4}$ is $- 890 k J m o l^{- 1}$ and standard enthalpy of vaporisation of water is 40.5 kJ $m o l^{- 1}$ . Calculate the enthalpy change for the reaction :
$C H_{4 (g)} + 2 O_{2 (g)} \to C O_{2 (g)} + 2 H_{2} O_{(g)}$

$- 890 k J m o l^{- 1}$
$- 809 k J m o l^{- 1}$
$809 k J m o l^{- 1}$
$- 971 k J m o l^{- 1}$

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Q. What is

△ U

when 2.0 mole of liquid water vaporises at

100^{\circ} ?

The heat of vaporisation,

△ H

vap. of water at

100^{\circ} C

40.66

k J m o l^{- 1}

60
75.11
88.2
59

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The enthalpies for the following reactions at 25°C are given.
$\frac{1}{2} H_{2} (g) + \frac{1}{2} O_{2} (g) \to O H (g); △ H = 10.06 K c a l$
$H_{2} (g) \to 2 H (g); △ H = 104.18 K c a l$
$O_{2} (g) \to 2 O (g); △ H = 118.32 K c a l$

Calculate the OH bond energy in the O - H group

100.19 K col
101.19 K col
-101.19 K col
-100.19 K col

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Q. The difference between the heats of a reaction at constant pressure and volume for the reaction

2 C_{6} H_{6} (l) + 15 O_{2} (g) \to 12 C O_{2} (g) + 6 H_{2} O (l)

at 25°C in kJ is:

$- 7.43 k J$
$- 4.43 k J$
$- 1.43 k J$
None of the above

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Q. Calculate the hydration enthalpy of ions for

N a C l (s)

from the following data.

Δ_{l a t t i c e} H = + 788 k J m o l^{- 1}

Δ_{s o l} H = + 4 k J m o l^{- 1}

$- 784 k J m o l^{- 1}$
$- 1084 k J m o l^{- 1}$
$+ 784 k J m o l^{- 1}$
$+ 1084 k J m o l^{- 1}$

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Q. Point out the wrong statement in relation to enthalpy

It is a state function
It is an intensive property
It is independent of the path followed for the change
Its value depends upon the amount of substance in the system

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Q. The difference between

C_{p}

and

C_{v}

can be derived from

H = U + P V

. Calculate the difference between

C_{p}

and

C_{v}

for 7.5 moles of an ideal gas.

$82.36$ $J m o l^{- 1} K^{- 1}$
$72.36$ $J m o l^{- 1} K^{- 1}$
$62.36$ $J m o l^{- 1} K^{- 1}$
$52.36$ $J m o l^{- 1} K^{- 1}$

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Q. Ethyl chloride

(C_{2} H_{5} C l)

is prepared by reaction of ethylene with hydrogen chloride:

C_{2} H_{4} (g) + H C l (g) \to C_{2} H_{5} C l (g) △ H = - 72.3 k J / m o l

What is the value of

△ U

(in

k J

), if

98 g

of ethylene and 109.5 g of

H C l

are allowed to react at

300 K

$- 64.81$
$- 190.71$
$- 209.41$
$- 224.38$

View Solution

(Δ H - Δ U)

for the formation of carbon monoxide

(C O)

from its elements at

298 K

(R = 8.314 J K^{- 1} {mol}^{- 1})

$1238.78 J {mol}^{- 1}$
$- 2477.57 J {mol}^{- 1}$
$2477.57 J {mol}^{- 1}$
$- 1238.78 J {mol}^{- 1}$

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Q. The dissociation energy of

C H_{4}

is 400 Kcal

m o l^{- 1}

and that of ethane is 670 Kcal

m o l^{- 1}

. The C - C bond energy is.

270 kcal
70 kcal
200 kcal
240 kcal

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Q. At

500

kilobar pressure density of diamond and graphite are

3 g / c c

and

2 g / c c

respectively, at certain temperature 'T'. Find the value of

| Δ H - Δ U | (k J / m o l e)

for the conversion of 1 mole of graphite to 1 mole of diamond at temperature 'T'.

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Q. The enthalpy change involved in the oxidation of glucose is 2880 kJ/mol.

25 %

of this energy is available for muscular work. If 100 kJ of muscular work is required to walk 1 km, calculate the maximum distance that can be covered by a person who as consumed 120 g of glucose

7.9 km
9.7 km
4.8 km
8.4 km

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Q. For the combustion of 1 mole of liquid benzene at

25^{\circ} C

, the heat of the reaction at constant pressure is given by,

C_{6} H_{6} (l) + 7 \frac{1}{2} O_{2} (g) ⟶ 6 C O_{2} (g) + 3 H_{2} O (l)

Δ H = - 780980 c a l

What would be the heat of the reaction at constant volume?

$781080 c a l$
$- 780900 c a l$
$780000 c a l$
$- 780086 c a l$

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Q. In the process shown in the figure for an ideal diatomic gas, the value of q and

Δ H

respectively are:

$79.5 P_{1} V_{1} and 94.5 P_{1} V_{1}$
$54.5 P_{1} V_{1} and 94.5 P_{1} V_{1}$
$9 P_{1} V_{1} and 0$
$79.5 P_{1} V_{1}$ and defined $(∵ P varies)$

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Q. One mole of a liquid (

1 b a r, 100 m l

) is taken in an adiabatic container and the pressure increases steeply to

100 b a r

. Then at constant pressure of

100 b a r

, volume decrases by

1 m L

. Calculate

Δ H

$500 J$
$990 J$
$650 J$
$720 J$

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Consider an endothermic reaction $X \to Y$ with the activation energies $E_{b}$ and $E_{f}$ for the backward and forward reactions, respectively. IN general

There is no definite relation between $E_{b} a n d E_{f}$
$E_{b} = E_{f}$
$E_{b} > E_{f}$
$E_{b} < E_{f}$

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