Heat of Forma...

Heat of Formation

Trending Questions

Q. Which one of the following

0.10 M

aqueous solutions will exhibit the largest freezing point depression ?

$K H S O_{4}$
glycine
glucose
hydrazine

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Q. A 0.1 molal aqueous solution of a weak acid is 30% ionized. If

K_{f}

for water is

1 {.86}^{\circ} C / m

, the freezing point of the solution will be

$- {0.18}^{\circ} C$
$- {0.54}^{\circ} C$
$- {0.24}^{\circ} C$
$- {0.36}^{\circ} C$

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The enthalpies of combustion of carbon and carbon monoxide are $- 393.5$ and $- 283 k J m o l^{- 1}$ respectively. The enthalpy of formation of carbon monoxide per mole is

−676.5 kJ
676.5 kJ
110.5 kJ
−110.5 kJ

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The enthalpy of combustion of methane, graphite and dihydrogen at 298 K are, $- 890.3 k J m o l^{- 1} - 393.5 k J m o l^{- 1}$ , and $- 285.8 k J m o l^{- 1}$ respectively. Enthalpy of formation of $C H_{4 (g)}$ will be
(i) $- 74.8 k J m o l^{- 1}$
(ii) $- 52.27 k J m o l^{- 1}$
(iii) $+ 74.8 k J m o l^{- 1}$
(iv) $+ 52.26 k J m o l^{- 1}$

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Explain why Cu⁺ ion is not stable in aqueous solutions?

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0.5

molal aqueous solution of a weak acid (HX) is

20 %

ionised. If

K_{f}

for water is

1.86 {K kg mol}^{- 1}

, the lowering in freezing point of the solution is

$0.56 K$
$1.12 K$
$- 0.56 K$
$- 1.12 K$

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Enthalpy of combustion of carbon to $C O_{2}$ is $- 393.5 k J m o l^{- 1}$ . Calculate the heat released upon formation of 35.2 g of $C O_{2}$ from carbon and dioxygen gas.

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Q. The species which by definition has ZERO standard molar enthalpy of formation at 298 K is

Br₂(g)
Cl₂(g)
H₂O(g)
CH₄(g)

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Q. The enthalpy of hydrogenation of cyclohexene is

- 119.5 k J / m o l

. If resonance energy of benzene is

- 150.4 k J / m o l

then its enthalpy of hydrogenation would be:

$- 508.9 k J / m o l$
$- 208.1 k J / m o l$
$- 269.9 k J / m o l$
$- 358.5 k J / m o l$

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Q. The enthalpy of combustion of

H_{2} (g)

at 298 K to give

H_{2} O (g)

is -249 kJ mol

^{- 1}

and bond enthalpies of H-H and O-O are 433 kJ mol

^{- 1}

and 492 kJ mol

^{- 1}

respectively. The bond enthalpy of O-H is

$- 464 k J m o l^{- 1}$
$232 k J m o l^{- 1}$
$464 k J m o l^{- 1}$
$- 232 k J m o l^{- 1}$

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Q. A solution containing

62 g

ethylene glycol in

250 g

water is cooled to

- 10^{\circ} C .

K_{f}

for water is

1.86 K k g m o l^{- 1}

, the amount of water

(i n g)

separated as ice is

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Q. Calculate the amount of ethylene glycol to be added to

4 k g

of water to prevent it from freezing at

- 6^{\circ} C

(K_{f} for water = 1.85 K k g m o l^{- 1})

$804.3 g$
$420.4 g$
$120.4 g$
$320.4 g$

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Different example of state, phase and component.

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Q. The bond dissociation energy of gaseous

H_{2}, C l_{2}

and HCl are 104, 58 and 103

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

respectively. The enthalpy of formation for

H C l

gas will be

$- 22.0 k c a l$
$- 44.0 k c a l$
$22.0 k c a l$
$44.0 k c a l$

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Q. The standard heats of formation of

C C l_{4} (g), H_{2} O (g), C O_{2} (g) a n d H C l (g) a t 298 K a r e - 25.5, - 57.8, - 94.1 a n d - 22.1 k c a l m o l^{- 1} r e s p e c t i v e l y . Δ H^{0} (298 K) f o r t h e r e a c t i o n

C C l_{4} (g) + 2 H_{2} O (g) \to C O_{2} (g) + 4 H C l (g)

$+ 82.8 k c a l m o l^{- 1}$
$- 82.8 k c a l m o l^{- 1}$
$+ 41.4 k c a l m o l^{- 1}$
$- 41.4 k c a l m o l^{- 1}$

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Why is LiF almost insoluble in water whereas LiCl soluble not only in water but also in acetone?

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Q. Given N₂ +3H2 =2NH3 and standard enthalpy is -92.4kj/mol
Then find the standard enthalpy of formation of nh3 gas

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Can enthalpy of formation be negative or positive?

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Q. What is ionic equilibrium?

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Q. When 12.2 g of benzoic acid is dissolved in 100 g of water, the freezing point of solution was found to be

- {0.93}^{o} C (K_{f} (H_{2} O) = 1.86 K k g m o l^{- 1})

. Then the number (n) of benzoic acid molecules associated (assuming 100% association) is

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Q. The

Δ_{f} H^{0}

for

C O_{2} (g), C O (g) a n d H_{2} O (g)

are -393.5, -110.5 and -241.8

k J m o l^{- 1}

respectively. The standard enthalpy change (in

k J m o l^{- 1}

) for the reaction

C O_{2} (g) + H_{2} (g) \to C O (g) + H_{2} O (g)

is :

524.1
+ 41.2
-262.5
- 41.2

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Q. Calculate the enthalpy of formation of

M g F_{2}

from thefollowing data-
Enthalpy of sublimation for

M g (s) \to M g (g) = 146.4 k J m o l^{- 1}

Enthalpy of dissociation of

F_{2} (g) \to 2 F (g) = 155.8 k J m o l^{- 1}

Ionisation energy of

M g (g) \to M g^{2 +} (g) = 2186 k J m o l^{- 1}

Electron gain enthalpy of

2 F \to 2 F^{- 1} = 2 \times - 322.6 = - 645.2 k J m o l^{- 1}

Lattice enthalpy of

M g F_{2} = - 2922.5 k J m o l^{- 1}

$- 1079.5 k J m o l^{- 1}$
$2200 k J m o l^{- 1}$
$1099.5 k J m o l^{- 1}$
$2200 k J m o l^{- 1}$

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Q. Nitrobenzene freezes at

278.98^{\circ} C

. If

0.25

molal solution of a solute in nitrobenzene causes freezing point depression of

2^{\circ} C

, then

K_{f}

(in

{K kg mol}^{- 1}

) for nitrobenzene is:

$2 {K kg mol}^{- 1}$
$4 {K kg mol}^{- 1}$
$8 {K kg mol}^{- 1}$
$6 {K kg mol}^{- 1}$

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If the freezing point of a 0.01 molal aqueous solution of a cobalt chloride ammonia complex ( which behaves as a strong electrolyte ) is 0.0558 degree Celsius, the number of chloride in the coordination sphere of the complex is ? (kf of water = 1.86k kg/mole

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Q. The standard heats of formation of

N O_{2}

(g) and

N_{2} O_{4}

(g) are

8.0

and

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

respectively, the heat of dimerization of

N O_{2}

k c a l

$10.0$
$- 6.0$
$- 12.0$
$- 14.0$

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Q. The freezing point of a solution containing

50 {cm}^{3}

of ethylene glycol in

50 g

of water is found to be -34°C. Assuming ideal behaviour, calculate the density of ethylene glycol in

{g/cm}^{3}

(K_{f} for water = 1.86 {K Kg mol}^{- 1})

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Why do diamonds and graphite, the two allotropic forms of carbon evolve different amounts of heat on combustion?

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Q. Using the data provided, calculate the multiple bond energy

(k J m o l^{- 1})

of a

C \equiv C

bond in

C_{2} H_{2} .

Given that the heat of formation of

C_{2} H_{2} = 225 k J m o l^{- 1} .

(take the bond energy of

C - H

bond as

350 k J m o l^{- 1}

2 C (s) \to 2 C (g) △ H = 1410 k J m o l^{- 1}

H_{2} (g) \to 2 H (g) △ H = 330 k J m o l^{- 1}

1165
837
815
865

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Q. Calculate the heat of formation of acetic acid from the following data.

C H_{3} C O O H (l) + 2 O_{2} (g) \to 2 C O_{2} (g) + 2 H_{2} O (l), △ H = - 207.9 K c a l

C (s) + O_{2} (g) \to C O 2 (g) △ H = - 94.48 K c a l

H_{2} (g) + \frac{1}{2} O_{2} (g) \to H_{2} O (l) △ H = - 68.4 K c a l

117.86 K cal
-117.86 K cal
116.86 K cal
-116.86 K cal

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Q. In the reaction

C S_{2} (l) + 3 O_{2} (g) \to C O_{2} (g) + 2 S O_{2} (g) △ H = - 265 k c a l

The enthalpies of formation of

C O_{2}

and

S O_{2}

are both negative and are in the ratio 4 : 3. The enthalpy of formation of

C S_{2}

is + 26 kcal/mol. Calculate the enthalpy of formation of

S O_{2} .

- 90 kcal/mol
-52 kcal/mol
-78 kcal/mol
-71.7 kcal/mol

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