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Enthalpy

Enthalpy

Trending Questions

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

$Δ U = 0, Δ S_{total} \neq 0$
$Δ U = 0, Δ S_{total} = 0$
$Δ U = 0, Δ S_{total} = 0$
$Δ U \neq 0, Δ S_{total} \neq 0$

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Q.

Calculate the enthalpy change on freezing of 1.0 mol of water at ${10.0}^{\circ} C$ to ice at $- {10.0}^{\circ} C . Δ f u s H = 6.03 k J m o l^{- 1} a t 0^{\circ} C$ .
$(C_{p} [H_{2} O (l)] = 75.3 J m o l^{- 1} K^{- 1}$
$C_{p} [H_{2} O (s)] = 36.8 J m o l^{- 1} K^{- 1}$

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Q. One mole of an ideal gas at 300 K in thermal contact with surroundings expands isothermally from 1.0L to 2.0L against a constant pressure of 3.0 atm. In this process, the change in entropy of surroundings

(Δ S) i n T^{- 1}

is (1 L atm = 101.3J)

-5.763
5.763
1.013
-1.013

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Q.

A solution of two components containing $n_{1}$ moles of the $1^{s t}$ component and $n_{2}$ moles of the second component is prepared. $M_{1}$ and $M_{2}$ are the molecular weights of component $1$ and $2$ respectively. If $d$ is the density of the solution in $g {mL}^{- 1}$ , $C_{2}$ is the molarity and $x_{2}$ is the mole fraction of the $2^{n d}$ component, then $C_{2}$ can be expressed as:

$C_{2} = \frac{1000 x_{2}}{M_{1} + x_{2} (M_{2} - M_{1})}$
$C_{2} = \frac{d x_{2}}{M_{2} + x_{2} (M_{2} - M_{1})}$
$C_{2} = \frac{d x_{1}}{M_{2} + x_{2} (M_{2} - M_{1})}$
$C_{2} = \frac{1000 d x_{2}}{M_{1} + x_{2} (M_{2} - M_{1})}$

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Q.

Polymerisation of ethene to poly - ethene is represented by the equation
$n (C H_{2} = C H_{2}) \to (- C H_{2} - C H_{2} -)_{n}$
Given that average enthalpies of C = C and C - C bonds at 298 K are 590 and 331 kJ $m o l^{- 1}$ respectively, predict the enthalpy change when 56g of ethene changes to polyethylene.

144 kJ
-144 kJ
72 kJ
-72 kJ

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Q. Consider the following liquid – vapour equilibrium.

L i q u i d ⇌ V a p o u r

Which of the following relations is correct?

$\frac{d I n P}{d T^{2}} = \frac{- Δ H_{v}}{T^{2}}$
$\frac{d I n P}{d T} = \frac{- Δ H_{v}}{R T}$
$\frac{d I n G}{d T^{2}} = \frac{Δ H_{v}}{R T^{2}}$
$\frac{d I n P}{d T} = \frac{Δ H_{v}}{R T^{2}}$

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Q. For silver

C_{p} (J K^{- 1} m o l^{- 1}) = 23 + 0.01 T

. If the temperature (T) of 3 moles of silver is raised from 300 K to 1000 K at 1 atm pressure, the value of

Δ H

will be close to:

13 kJ
62 kJ
16 kJ
21 kJ

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Q.

Define bond enthalpy and bond dissociation enthalpy

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Q. Calculate the lattice enthalpy of

C a C l_{2}

, given that :
Enthalpy of sublimation for

C a (s) \to C a (g) = 121 k J m o l^{- 1}

Enthalpy of dissociation of

C l_{2} (g) \to 2 C l (g) = 242.8 k J m o l^{- 1}

Ionisation energy of

C a (g) \to C a^{+ +} (g) = 2422 k J m o l^{- 1}

Electron gain enthalpy of

2 C l \to 2 C l^{- 1} = (2 \times - 355) k J m o l^{- 1} = - 710 k J m o l^{- 1}

Enthalpy of formation of

C a C l_{2} = - 795 k J m o l^{- 1}

$- 2670.8 k J m o l^{- 1}$
$- 2870.8 k J m o l^{- 1}$
$- 2770.8 k J m o l^{- 1}$
$- 2970.8 k J m o l^{- 1}$

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Q. White phosphorous is a tetra atomic solid

[P_{4} (s)]

at room temperature and on strong heating in absence of oxygen, it polymerizes into red phosphorus as:

Δ H = - 104 kJ/mol of P_{4}

The enthalpy of sublimation

[P_{4} (s) \to P_{4} (g)]

white is

59 kJ/mol

and enthalpy of atomization is

316.25 kJ/mol

of

P (g)

.
Now find the average

P - P

bond enthalpy in

P_{4}

molecule is:

$102 kJ$
$201 kJ$
$104 kJ$
$120 kJ$

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Q. The relation between

Δ E a n d Δ H

is

$Δ H = Δ E - P Δ V$
$Δ H = Δ E + P Δ V$
$Δ E = Δ V + Δ H$
$Δ E = Δ H + P Δ H$

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Q. For combustion of one mole of magnesium in an open container at

300 K

and 1 bar pressure,

Δ_{c} H^{⊖} = - 601.70 k J m o l^{- 1}

, the magnitude of change in internal energy for the reaction is ____ kJ.
(Nearest integer)
(Given :

R = 8.3 J K^{- 1} {mol}^{- 1}

)

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Q.

The enthalpies of all elements in their standard states are?

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Q. Boiling point of 0.01 M AB2 which is 10%dissociated in aqueous medium (Kb = 0.52) as A2 and B(1) 273.006 K(2) 373.006 K(3) 0.006 k(4) 272.006

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Q.

Standard Molar Enthalpy of Formation of ${CO}_{2}$ Is equal to

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Q.

Calculate enthalpy change for the change $8 S_{(g)} \to S_{8 (g)^{'}}$ given that
$H_{2} S_{2 (g)} \to 2 H_{(g)} + 2 S_{(g)}, Δ H = 239.0 k c a l m o l^{- 1} H_{2} S_{2 (g)} \to 2 H_{(g)} + S_{(g)}, Δ H = 175.0 k c a l m o l^{- 1}$

-508.0 k cal
- 512.0 k cal
508.0k cal
+ 512.0 k cal

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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

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

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Q. 5 moles of oxygen are heated at constant volume from

10^{\circ} C t o 20^{\circ} C .

What will be the change in the internal energy of gas?
(The molar heat of oxygen at constant pressure,

C_{p} = 7.03

cal mol

^{- 1}

K

^{- 1}

and

R = 8.31 J

mol

^{- 1} K^{- 1}

)

$352 c a l$
$252 c a l$
$452 c a l$
$152 c a l$

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Q. The enthalpy of vapourization of liquid is

30 k J m o l^{- 1}

and entropy of vaporization is

75 k J / m o l

. The boiling point of the liquid at 1 atm is

250 K
400 K
450 K
600 K

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Q.

When we add ice to water it becomes cold. Explain.

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Q. Difference between

△ H

and

△ U

for the combustion of benzene at 300 K is :

C_{6} H_{6} (l) + \frac{15}{2} O_{2} (g) \to 6 C O_{2} (g) + 3 H_{2} O (l)

10.48 kJ
3.74 kJ
14.86 kJ
6.73 kJ

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Q.

An ideal monoatomic gas of two moles occupying a volume V at $27 ° C$ .Gas expanding adiabatically having volume $2 V .$ calculate (a)the final temperature of the gas and (b) change in its internal energy.

(a) $189$ K (b) $- 2.7$ kJ
(a) $195$ K (b) $2.7$ kJ
(a) $189$ K (b) $2.7$ kJ
(a) $195$ K (b) $- 2.7$ kJ

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Q.

Explain what happens to the molecular motion and energy of $1 kg$ of water at $273 k$ when it changes to the ice at the same temperature. How is the latent heat of fusion related to the energy exchange that takes place during this change of state?

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Q. Calculate the lattice enthalpy in

k J m o l^{- 1}

of

L i F

given that
Sublimation of lithium is

155.3 k J m o l^{- 1}

Dissociation of half mole of

F_{2} = 75.3 k J

Ionization enthalpy of lithium

= 520 k J m o l^{- 1}

Electron gain enthalpy of 1 mol of

F (g) = - 333 k J Δ_{f} H_{o v e r a l l} = - 594 k J m o l^{- 1}

$- 1200.4 {kJ mol}^{- 1}$
$- 1488.6 {kJ mol}^{- 1}$
$- 1011.6 {kJ mol}^{- 1}$
$- 984.6 {kJ mol}^{- 1}$

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Q.

Assertion: Hydrogen gas has the highest calorific value.

Reason: Hydrogen is the lightest gas and hence produces a large amount of heat.

Both ‘A’ and ‘R’ are correct and ‘R’ is the correct explanation of ‘A’.
Both ‘A’ and ‘R’ are correct, but ‘R’ is not the correct explanation of ‘A’.
‘A’ is correct, but ‘R’ is incorrect
‘A’ is incorrect, but ‘R’ is correct

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Q.

The enthalpies of elements in their standard states are taken as zero. The enthalpy of formation of a compound
(a) is always negative
(b) is always positive
(c) may be positive or negative
(d) is never negative

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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. 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. The heat for a reaction,

C_{10} H_{8} (s) + 12 O_{2} (g) \to 10 C O_{2} (g) + 4 H_{2} O (l)

at constant volume is given as

- 1228.2 k c a l

at

25^{o} C

. The heat of the reaction at constant pressure and same temperature is:

$- 1345.5 k c a l$
$- 1229.3 k c a l$
$- 1156 k c a l$
$- 1380.2 k c a l$

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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

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

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