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Questions and Answers
What is the hybridization of the orbitals in alkanes?
What is the hybridization of the orbitals in alkanes?
- sp3 hybridization (correct)
- sp2 hybridization
- sp hybridization
- d2sp3 hybridization
What is the bond angle in the tetrahedral arrangement of sp3 hybridized carbon in alkanes?
What is the bond angle in the tetrahedral arrangement of sp3 hybridized carbon in alkanes?
- 180º
- 90º
- 109.5º (correct)
- 120º
Why is the process of promoting an electron to a p orbital considered favourable?
Why is the process of promoting an electron to a p orbital considered favourable?
- It results in a complete valence shell.
- It creates more stable ionic bonds.
- It allows for unpaired electrons which reduce repulsion. (correct)
- It leads to a decrease in total energy.
What is the electronic configuration of carbon before hybridization?
What is the electronic configuration of carbon before hybridization?
What type of bond is formed between the sp3 orbital of carbon and the 1s orbital of hydrogen in alkanes?
What type of bond is formed between the sp3 orbital of carbon and the 1s orbital of hydrogen in alkanes?
What is produced from every carbon and two hydrogen atoms in a hydrocarbon during combustion?
What is produced from every carbon and two hydrogen atoms in a hydrocarbon during combustion?
Which of the following emissions from internal combustion engines does NOT contribute to acid rain?
Which of the following emissions from internal combustion engines does NOT contribute to acid rain?
What is the primary function of a catalytic converter in vehicles?
What is the primary function of a catalytic converter in vehicles?
What happens when leaded petrol passes through a catalytic converter?
What happens when leaded petrol passes through a catalytic converter?
Which process involves the unequal splitting of shared electron pairs in covalent bonds?
Which process involves the unequal splitting of shared electron pairs in covalent bonds?
Which bond is broken first in a reaction involving alkanes and chlorine?
Which bond is broken first in a reaction involving alkanes and chlorine?
What is produced when a methyl radical reacts with a chlorine molecule?
What is produced when a methyl radical reacts with a chlorine molecule?
What role do free radicals play in the reaction between alkanes and chlorine?
What role do free radicals play in the reaction between alkanes and chlorine?
What happens during the termination step in the reaction involving free radicals?
What happens during the termination step in the reaction involving free radicals?
Why are free radicals considered very reactive?
Why are free radicals considered very reactive?
What is the primary role of chlorine radicals in the reaction process?
What is the primary role of chlorine radicals in the reaction process?
Which of the following statements is NOT true about the reaction mechanism described?
Which of the following statements is NOT true about the reaction mechanism described?
What initiates the homolytic fission of covalent bonds to form free radicals?
What initiates the homolytic fission of covalent bonds to form free radicals?
What is formed as a result of termination when two chlorine radicals combine?
What is formed as a result of termination when two chlorine radicals combine?
What is the outcome when excess chlorine is used during the chlorination process?
What is the outcome when excess chlorine is used during the chlorination process?
Which product is primarily produced through the thermal cracking process?
Which product is primarily produced through the thermal cracking process?
Which condition is NOT associated with the thermal cracking process?
Which condition is NOT associated with the thermal cracking process?
What is the effect of fractional distillation in the context of chlorination reactions?
What is the effect of fractional distillation in the context of chlorination reactions?
What type of mechanism does catalytic cracking proceed through?
What type of mechanism does catalytic cracking proceed through?
Which of the following fractions is primarily used as aviation fuel?
Which of the following fractions is primarily used as aviation fuel?
What is the general formula for non-cyclic alkanes?
What is the general formula for non-cyclic alkanes?
What property allows for the separation of crude petroleum into fractions?
What property allows for the separation of crude petroleum into fractions?
Which type of fission is involved in the catalytic cracking process?
Which type of fission is involved in the catalytic cracking process?
Which of the following is NOT a use of alkanes?
Which of the following is NOT a use of alkanes?
What condition is necessary for thermal cracking to occur effectively?
What condition is necessary for thermal cracking to occur effectively?
What product can be formed from the cracking of heavy fractions?
What product can be formed from the cracking of heavy fractions?
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Study Notes
Structure of Alkanes
- Members of a homologous series.
- General formula is CnH2n+2 (for non-cyclic alkanes).
- Saturated hydrocarbons, meaning all carbon-carbon bonding is single.
- Bonds are spaced tetrahedrally about carbon atoms.
Physical properties of Alkanes
- Boiling point increases with increasing chain length (due to increased Van der Waals forces).
- Alkanes are insoluble in water (due to their non-polar nature).
- Alkanes are less dense than water.
Chemical properties of Alkanes
- Relatively unreactive due to strong C-H and C-C bonds.
- They undergo combustion reactions, releasing energy.
- They undergo substitution reactions, replacing hydrogen atoms with other atoms or groups.
Breaking covalent bonds
- Can occur via homolytic fission (producing radicals) or heterolytic fission (producing ions).
- The weakest bond is usually broken first.
- Energy to break bonds can come from heat or light.
Cracking
- Involves breaking C-C bonds in alkanes to convert heavier fractions into lighter, more useful products (like gasoline).
- Two types:
- Thermal cracking:
- Uses high pressure (7000 kPa) and high temperature (400°C - 900°C).
- Proceeds via a free radical mechanism.
- Produces mainly alkenes and hydrogen.
- Catalytic cracking:
- Uses zeolite catalyst, slight pressure, and high temperature (450°C).
- Proceeds via a carbocation (ionic) mechanism.
- Produces branched and cyclic alkanes, aromatic hydrocarbons.
- Thermal cracking:
Uses of Alkanes
- LPG is used as fuel for cooking and heating.
- Gasoline is used as fuel for cars.
- Naphtha is used to make petrochemicals.
- Kerosine is used as aviation fuel.
- Gas oil is used as central heating fuel.
- Lubricating oil is used for lubrication.
- Fuel oil is used as power station fuel and ship fuel.
- Wax and grease are used in candles and as grease for bearings.
- Bitumen is used in road surfaces and roofing.
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