Enthalpy of C...

Enthalpy of Combustion

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Q. When 1g of anhydrous oxalic acid is burnt at 25 ° C , the amount of heat liberated is 2.8 35 kJ. ∆H combustion is

Q. The heats of combustion of

C H_{4} & C_{4} H_{10}

are -890.3

k J m o l^{- 1} & - 2878.7 k J m o l^{- 1}

respectively. Which of the two has greater efficiency as fuel per gram?

Methane
Butane

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Q. When 5 litres of a gas mixture of methane and propane is perfectly combusted at

0^{\circ} C

and 1 atmosphere, 16 litres of oxygen at the same temperature and pressure is consumed. The amount of heat released from this combustion in

k J (Δ H_{c o m b .} (C H_{4}) = 890 k J m o l^{- 1}, Δ H_{c o m b .} (C_{3} H_{8}) = 2220 k J m o l^{- 1})

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The heat liberated on complete combustion of $7.8 g$ benzene is $327 K J$ . This heat has been measured at constant volume and at $27^{0} C$ . What is the heat of combustion of benzene at constant pressure at $27^{0} C (R = 8.3 J m o l^{- 1} K^{- 1})$

-3273.735 KJ
-3274.735 KJ
-3275.735 KJ
-3270.735 KJ

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Q. Heat of a reaction is defined as the amount of heat absorbed or evolved at a given temperature when the reactants have combined to form the products is represented by balanced chemical equation. If the heat is denoted by

q

then the numerical value of

q

depends on the manner in which
the reaction is performed for two methods of conducting chemical reactions in calorimeters.

The heat of combustion of maltose at a constant volume in the above question if water vapour is not condensed will be:

-1350 kcal/mol
-1343 kcal/mol
-1370 kcal/mol
-1400 kcal/mol

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The heat of combustion of ethylene at $18^{\circ} C$ and at constant volume is -335.8 K cal when water is obtained in liquid state. What is the heat of combustion at constant pressure and at $18^{\circ} C$ .

-337 k cal
337 k cal
237 k cal
-237k cal

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Q. Enthalpy for the reaction

C + O_{2} \to C O_{2}

Positive
Negative
Zero
Can't say, need thermochemical data

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Q. When 1 g of anhydrous oxalic acid is burnt at 25°C, the amount of heat liberated is 2.835 kJ. H combustion is (oxalic acid : C2H2O4) (1) –255.15 kJ (2) –445.65 kJ (3) –295.24 kJ (4) –155.16 kJ

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-3273.735 KJ
-3274.735 KJ
-3275.735 KJ
-3270.735 KJ

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Q. The heat of formation of

C O

and

C O_{2}

are

- 26.4

kcal and

- 94

kcal respectively. The heat of combustion of carbon monoxide will be:

$+ 26.4$ kcal
$- 67.6$ kcal
$- 120.4$ kcal
$+ 52.8$ kcal

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A B

A_{2}

and

B_{2}

are diatomic molecules. If the bond enthalpies of

A_{2}, A B

and

B_{2}

are in the ratio 1 : 1 : 0.5 respectively and enthalpy of formation of

A B

from

A_{2}

and

B_{2}

- 100 {kJ/mol}^{- 1}

. What is the bond enthalpy of

A_{2}

$400 kJ/mol$
$200 kJ/mol$
$100 kJ/mol$
$300 kJ/mol$

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Q. Combustion of glucose is according to the following reaction

C_{6} H_{12} O_{6} (s) + 6 O_{2} (g) \to 6 C O_{2} (g) + 6 H_{2} O (l); Δ H = - 2900 k J

How much heat energy if evolved in the combustion of 1.8g of glucose?

15.2 kJ
8.47 kJ
29 kJ
None

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Q. Enthalpy of is always exothermic.

formation
combustion
solution
neutralisation

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Q. In the combustion of

2 g

of methane,

25 k c a l

heat is liberated. Find the molar heat of combustion of methane.

$100 k c a l$
$200 k c a l$
$75 k c a l$
$150 k c a l$

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Q. Efficiency of a fuel is based on it's :

Specific heat
Calorific value
Cost
Ignition temperature

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Q. When a certain amount of ethylene was combusted,

6226 kJ

heat was evolved. If heat of combustion of

1

mole of ethylene is

1411 kJ

, the volume of

O_{2}

(at NTP) that entered into the reaction is:

$296.5 mL$
$296.5 litres$
$6226 \times 22.4 litres$
$22.4 litres$

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Q. The energy of combustion of propane

(C_{3} H_{8})

gas in terms of given data is:
Bond energy (kJ/mol)

\begin{matrix} ϵ_{C - H} & ϵ_{O = O} & ϵ_{C = O} & ϵ_{O - H} & ϵ_{C - C} + x_{1} & + x_{2} & + x_{3} & + x_{4} & + x_{5} \end{matrix}

Resonance energy of

C O_{2}

- z k J / m o l

and

△ H_{v a p o r i z a t i o n} [H_{2} O] i s y k J / m o l

$8 x_{1} + 2 x_{5} + 5 x_{2} - 6 x_{3} - 8 x_{4} - 4 y - 3 z$
$6 x_{1} + x_{5} + 5 x_{2} - 3 x_{3} - 4 x_{4} - 4 y - 3 z$
$8 x_{1} + 2 x_{5} + 5 x_{2} - 6 x_{3} - 8 x_{4} - y - z$
$8 x_{1} + 2 x_{5} + 5 x_{2} - 6 x_{3} - 8 x_{4} + 4 y + 3 z$

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Q. The work done during combustion of

9 \times 10^{- 2} K g

of ethane,

C_{2} H_{6}

(g) at 300 K is:
(Given: R 8.314 J

d e g^{- 1}, m o l^{- 1}

, atomic mass C = 12, H = 1)

+6.236 kJ
- 6.236 kJ
- 18.71 kJ
+18.71 kJ

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Q. Energy required to dissociate 4 g of gaseous hydrogen into free gaseous atoms is 208 Kcal at

25^{\circ} C

. The bond energy of H-H bond per mole will be

104 K cal
10.4 K cal
1040 K cal
104.2 k cal

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Q. The value of

{log}_{10} K

for a reaction

A ⇌ B

is:

Given : △_{r} H_{298 K}^{\circ} = - 54.07 k J m o l^{- 1}, △_{r} S_{298 K}^{\circ} = 10 J K^{- 1} m o l^{- 1}

and

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

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The standard heat of combustion of $A l$ is $- 837.8 k J m o l^{- 1}$ $25^{\circ} C$ which of the following releases $250 k c a l$ of heat?

The reaction of $0.624 m o l$ of $A l$
The formation of $0.624 m o l$ of $A l_{2} O_{3}$
The reaction of $0.312 m o l$ of $A l$
The formation of $0.150 m o l$ of $A l_{2} O_{3}$

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Q. The heat of combustion of sucrose

(C_{12} H_{22} O_{11})

- 5.65 \times 10^{3} k J

. If complete combustion of

1.0 k g

sucrose is done, heat evloved will be:

$1.65 \times 10^{4} k J$
$5.65 \times 10^{3} k J$
$7.38 \times 10^{5} k J$
$3.51 \times 10^{5} k J$

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Q. The standard heat of combustion of solid boron is equal to

$Δ H_{f}^{0} (B_{2} O_{3})$
$\frac{1}{2} Δ H_{f}^{0} (B_{2} O_{3})$
$2 Δ H_{f}^{0} (B_{2} O_{3})$
$- \frac{1}{2} Δ H_{f}^{0} (B_{2} O_{3})$

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