Thermal Decomposition of Alkanes

Q. Aldol condensation product of acetone on dehydration gives

1. but-2-en-al
2. 2-methylpent-3-en-4-one
3. 4-hydroxy-4-methylpentane-2-one
4. 4-methylpent-3-en-2-one

Q. Which of the following do not give aldol reaction with dil. NaOH?

1. $C{H}_{3}CHO$
2. $C{H}_{3}C{H}_{2}C{H}_{2}CHO$
3. $C{H}_{3}C{H}_{2}CHO$
4. $PhCHO$

Q. What is the order of heat of combustion of the following ?
(i) Heptane
(ii) Pentane
(iii) 2-Methyl pentane
(iv) 2, 2-Dimethyl butane

1. (i) > (ii) > (iii) > (iv)
2. (iv) > (iii) > (ii) > (i)
3. (i) > (iii) > (iv) > (ii)
4. (i) > (iii) > (ii) > (iv)

Q. Carbon black, which is used in making printer's ink, is obtained by decomposition of

1. Acetylene
2. Carbon tetrachloride
3. Methane
4. Benzene

Q.

The enthalpy of combustion of methane, graphite and dihydrogen at 298 K are, –890.3 kJ mol^–1 –393.5 kJ mol^–1, and –285.8 kJ mol^–1 respectively. Enthalpy of formation of CH_4(g) will be

(i) –74.8 kJ mol^–1 (ii) –52.27 kJ mol^–1

(iii) +74.8 kJ mol^–1 (iv) +52.26 kJ mol^–1.

Q.

Carbon black, used in making printer’s ink, is obtained by decomposition of

1. Carbon tetrachloride

2. methane

3. Benzene

4. acetylene

Q.

The standard enthalpy of combustion at 25∘ C of hydrogen, cyclohexene (C6H10) and cyclohexane (C6H12) are -241, -3800 and -3920 KJ/mole respectively. Calculate the heat of hydrogenation of cyclohexene.

Q. In the process of cracking

1. Organic compounds decompose into their constituent elements
2. Hydrocarbons decompose into carbon and hydrogen
3. Hydrocarbons yield alkyl radicals and hydrogen
4. High molecular weight organic compounds decompose to give low molecular weight organic compounds

Q. Why the iodination of alkane is endothermic but chlorination and bromination are exothermic ?

Q. Type: Multiple Correct answers
The heat evolved in the combustion of benzene is given by
C_{​​​​​​6}​​​​​H_​6(l)+15/2O₂(g)----------->3H₂O(l)+6CO₂(g)
∆H=-781.0kcal mol^{​​​​-1
​​​​​​}When 156 g of C₆H_{​​​​6} is burnt in an open container the amount of heat energy released will be
a)150.2 kcal mol^{​​​​-1} b)1562.0 kcal mol^{​​​​-1}
c)6528.2 kJ mol-1^​​-1 d)2448.5 kJ mol^{​​​​-1}

Q.

A hydro carbon C10Hx requires 40 moles of O2 for combustion of 2.5moles. Calculate value of" X"

Q. Thermal decomposition of higher hydrocarbons into lower hydrocarbons is called:

1. reforming
2. isomerization
3. aromatization
4. cracking

Q. A mixture of ethane and ethene occupies 41 L at 1 atm and 500k the mixture reacts completely with 10/3 moles of O2 to produced CO2 and H2O . The mole fraction of ethane and ethene in the mixture are ?

Q. The process in which higher hydrocarbons are broken down into lower hydrocarbons by controlled pyrolysis, is called

1. Hydrolysis
2. Cracking
3. Oxidation

4. Reduction

Q. Thermal decomposition of alkanes in the absence of air is called:

1. Cracking
2. Oxidation
3. Cumbustion
4. Hydrogenation

Q. How many moles of oxygen will react with $1$ mole of an aliphatic compound $C_3{H}_8$? The reaction is given as:
$C_3{H}_8+O_2\left(Excess\right)\to C{O}_2+H_{2}O$

1. $5\text{mol}$
2. $2\text{mol}$
3. $3\text{mol}$
4. $8\text{mol}$

Q. Name the reaction
$C_{10}{H}_{22}\stackrel{900K}{\to }{C}_4{H}_8+C_6{H}_{14}$

1. Alkylation

2. Cracking

3. Pyrolysis
4. Fractionation

Q. Pyrolysis of methane is known as:

1. cracking
2. thermal cracking
3. thermolysis
4. All of these

Q. Name the reaction
$C_{10}{H}_{22}\stackrel{900K}{\to }{C}_4{H}_8+C_6{H}_{14}$

1. Alkylation

2. Cracking

3. Pyrolysis
4. Fractionation

Q.

Choose the correct words or phrases from the brackets to complete the following sentences:
The reaction proceeds in Habers process is an _____ and reversible. (endothermic/exothermic)

Q. What happens in carbonization process?

1. Hydrolysis
2. Electrolysis
3. Pyrolysis
4. All of the above

Q. Write a short note on cracking.

Q.

With increase in number of carbon atoms in alkanes, heat of combustion:

1. does not change
2. changes cant be predicted
3. decreases
4. increases

Q. $1$ mole of an aliphatic compound $C_3{H}_8$ is completely burnt in an excess of $O_2$. How many moles of oxygen reacted?

1. $5\text{mol}$
2. $2\text{mol}$
3. $3\text{mol}$
4. $8\text{mol}$

Q. ​The order of energy released on combustion of the following fuels per litre is
a) LPG > octane > liquid hydrogen > gaseous hydrogen
b) liquid hydrogen > gaseous hydrogen > LPG > octane
c) octane > LPG > liquid hydrogen > gaseous hydrogen
d) gaseous hydrogen > liquid hydrogen > octane > LPG

Q. Write the structures of all possible alkanes and alkenes that would be produced on pyrolysis of $n-$butane.

Q. Explain the following process:

Q. Most of the chemical reactions in Cracking is based on:

1. Carbocation formation
2. Carbanion formation
3. Radical formation
4. Zwitter ion formation

Q. In the process of cracking

1. Organic compounds decompose into their constituent elements
2. Hydrocarbons decompose into carbon and hydrogen
3. High molecular weight organic compounds decompose to give low molecular weight organic compounds
4. Hydrocarbons yield alkyl radicals and hydrogen

Q. In cracking, reaction is propagated through:

1. absorption of hydrogen by the formed radical
2. release of hydrogen by the formed radical
3. gain of electrons by the formed radical
4. release of electron by formed radical