What is fractional distillation of crude oil?

A bond enthalpy is the energy required to break one mole of a specific covalent bond in the gaseous phase, averaged over different molecules containing that bond. Bond enthalpies are always endothermic (positive).

True or False? In a fractionating column, hydrocarbons with high boiling points are collected near the top of the column.

False. Hydrocarbons with high boiling points condense lower down the column where temperatures are higher. Low boiling point fractions rise further up and are collected nearer the top.

Why do hydrocarbons with longer chains have higher boiling points?

Longer chain molecules have more electrons, producing stronger instantaneous dipole-induced dipole (van der Waals') forces between molecules. More energy is needed to overcome these forces, so boiling points are higher.

What is a hydrocarbon fraction in the context of crude oil?

A hydrocarbon fraction is a group of hydrocarbons with similar chain lengths and therefore similar boiling points that are collected from the same region of the fractionating column during fractional distillation.

Fractional distillation is a .......... process, not a chemical reaction. The crude oil is first .......... so that most of it vaporises, and the vapours rise up the .......... column.

Fractional distillation is a physical process, not a chemical reaction. The crude oil is first heated so that most of it vaporises, and the vapours rise up the fractionating column.

True or False? Fractional distillation breaks covalent bonds in the hydrocarbon molecules to separate them.

False. Fractional distillation is a physical process. Only intermolecular forces (van der Waals') are overcome during vaporisation. Covalent bonds within the molecules remain intact.

What is cracking in organic chemistry?

A linear molecule is a molecule with two bonding pairs and no lone pairs on the central atom (or two lone pairs and two bonding pairs giving 180° bond angle), resulting in a bond angle of 180°. Examples include CO 2 and BeCl 2 .

True or False? Cracking is a physical process that separates hydrocarbons without breaking any covalent bonds.

False. Cracking is a chemical change that breaks C-C covalent bonds. This distinguishes it from fractional distillation, which only overcomes intermolecular forces.

In catalytic cracking, a temperature of around .......... °C and a .......... catalyst (such as a zeolite) are used. The main products are .......... and aromatic hydrocarbons.

In catalytic cracking, a temperature of around 450 °C and a zeolite (aluminosilicate) catalyst are used. The main products are motor fuels and aromatic hydrocarbons.

Write the equation for cracking decane to produce octane and ethene.

C 10 H 22 → C 8 H 18 + C 2 H 4 Decane is cracked over a zeolite catalyst to give octane (a useful fuel) and ethene (a valuable alkene).

Thermal cracking uses temperatures up to .......... °C and pressures up to .......... atmospheres. It produces mainly .......... and alkanes. No catalyst is used.

Thermal cracking uses temperatures up to 1000 °C and pressures up to 70 atmospheres. It produces mainly alkenes and alkanes. No catalyst is used.

True or False? Cracking produces only alkanes from longer-chain hydrocarbons.

False. Cracking produces both smaller alkanes and one or more alkene molecules. For example, decane cracked to octane and ethene; ethene is an alkene.

Why is cracking commercially important?

Supply of long-chain fractions from crude oil exceeds demand, while shorter alkanes and alkenes are in high demand as fuels and as feedstocks for polymer production. Cracking converts surplus low-value fractions into higher-value products.

In catalytic cracking, a temperature of around .......... °C and a .......... catalyst are used. The main products are .......... and aromatic hydrocarbons.

In catalytic cracking, a temperature of around 500 °C and a zeolite catalyst are used. The main products are branched alkanes and aromatic hydrocarbons.

What is complete combustion of an alkane?

Complete combustion occurs when an alkane burns in excess oxygen. All carbon atoms are fully oxidised to carbon dioxide and all hydrogen atoms are oxidised to water. No carbon monoxide or soot is produced.

True or False? Incomplete combustion of alkanes always produces carbon monoxide as the only carbon-containing product.

False. Incomplete combustion produces carbon monoxide and/or carbon (soot) depending on how limited the oxygen supply is. Both can form alongside water.

.......... C 8 H 18 + .......... O 2 → .......... CO 2 + .......... H 2 O

2 C 8 H 18 + 25 O 2 → 16 CO 2 + 18 H 2 O

How does carbon monoxide harm the body?

Carbon monoxide binds strongly to haemoglobin in red blood cells, reducing its ability to carry oxygen. This can cause dizziness, unconsciousness, and in severe cases, death.

In a car engine, nitrogen reacts with oxygen at high temperature to form .......... . This can be further oxidised in air to form .......... . Both dissolve in water to form ......... , contributing to acid rain.

In a car engine, nitrogen reacts with oxygen at high temperature to form NO (nitrogen monoxide) . This can be further oxidised in air to form NO 2 (nitrogen dioxide). Both dissolve in water to form nitric acid , contributing to acid rain.

State two reactions that occur in a catalytic converter and write the equation for each.

Oxidation of CO: 2CO + O 2 → 2CO 2 Reduction of NO: 2CO + 2NO → 2CO 2 + N 2 Platinum, palladium, and rhodium on a ceramic honeycomb provide the catalytic surface.

True or False? Flue gas desulfurisation using calcium carbonate produces calcium sulfate and carbon dioxide as products.

True. CaCO 3 + SO 2 (g) + ½O 2 (g) → CaSO 4 (s) + CO 2 (g). The calcium sulfate (gypsum) produced is a useful by-product.

Incomplete combustion

Incomplete combustion occurs when an alkane burns in a limited supply of oxygen , producing carbon monoxide and/or carbon (soot) alongside water, rather than carbon dioxide.

Define free radical .

A tetrahedral molecule is a molecule with four bonding pairs of electrons around the central atom and no lone pairs, giving a bond angle of 109.5°. Examples include CH 4 and CCl 4 .

In the initiation step of free-radical substitution, UV light causes .......... fission of the Cl–Cl bond, producing two .......... radicals.

In the initiation step of free-radical substitution, UV light causes homolytic fission of the Cl–Cl bond, producing two chlorine radicals.

True or False? In the propagation step of free-radical substitution, the halogen radical is consumed and not regenerated.

False. The halogen radical is regenerated in propagation, allowing a chain reaction to continue. A new alkyl radical attacks another halogen molecule to form a halogenoalkane and regenerate the halogen radical.

What are the three steps of free-radical substitution, in order?

Initiation Propagation Termination

The termination step occurs when two .......... collide and combine to form a single .......... molecule.

The termination step occurs when two free radicals collide and combine to form a single unreactive molecule.

True or False? Free-radical substitution of alkanes with chlorine produces a single pure halogenoalkane product.

False. A mixture of substitution products forms. If excess chlorine is present, multiple hydrogen atoms can be replaced, yielding a range of chlorinated compounds.

Define homolytic fission .

A trigonal planar molecule is a molecule with three bonding pairs and no lone pairs around the central atom, giving bond angles of 120° and a flat triangular shape. Examples include BF 3 and SO 3 .

Why does the reaction between an alkane and chlorine require UV light?

UV light provides the energy needed for homolytic fission of the Cl–Cl bond to generate chlorine radicals in the initiation step. Without it, the alkane is too unreactive to react.

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Alkanes (AQA A Level Chemistry): Flashcards

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FrontFractional Distillation of Crude Oil
What is fractional distillation of crude oil?

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Cards in this collection (30)

What is fractional distillation of crude oil?
A bond enthalpy is the energy required to break one mole of a specific covalent bond in the gaseous phase, averaged over different molecules containing that bond. Bond enthalpies are always endothermic (positive).
True or False?
In a fractionating column, hydrocarbons with high boiling points are collected near the top of the column.
False.
Hydrocarbons with high boiling points condense lower down the column where temperatures are higher. Low boiling point fractions rise further up and are collected nearer the top.
Why do hydrocarbons with longer chains have higher boiling points?
Longer chain molecules have more electrons, producing stronger instantaneous dipole-induced dipole (van der Waals') forces between molecules. More energy is needed to overcome these forces, so boiling points are higher.
What is a hydrocarbon fraction in the context of crude oil?
A hydrocarbon fraction is a group of hydrocarbons with similar chain lengths and therefore similar boiling points that are collected from the same region of the fractionating column during fractional distillation.
Fractional distillation is a .......... process, not a chemical reaction. The crude oil is first .......... so that most of it vaporises, and the vapours rise up the .......... column.
Fractional distillation is a physical process, not a chemical reaction. The crude oil is first heated so that most of it vaporises, and the vapours rise up the fractionating column.
True or False?
Fractional distillation breaks covalent bonds in the hydrocarbon molecules to separate them.
False.
Fractional distillation is a physical process. Only intermolecular forces (van der Waals') are overcome during vaporisation. Covalent bonds within the molecules remain intact.
What is cracking in organic chemistry?
A linear molecule is a molecule with two bonding pairs and no lone pairs on the central atom (or two lone pairs and two bonding pairs giving 180° bond angle), resulting in a bond angle of 180°. Examples include CO₂ and BeCl₂.
True or False?
Cracking is a physical process that separates hydrocarbons without breaking any covalent bonds.
False.
Cracking is a chemical change that breaks C-C covalent bonds. This distinguishes it from fractional distillation, which only overcomes intermolecular forces.
In catalytic cracking, a temperature of around .......... °C and a .......... catalyst (such as a zeolite) are used. The main products are .......... and aromatic hydrocarbons.
In catalytic cracking, a temperature of around 450 °C and a zeolite (aluminosilicate) catalyst are used. The main products are motor fuels and aromatic hydrocarbons.
Write the equation for cracking decane to produce octane and ethene.
C₁₀H₂₂ → C₈H₁₈ + C₂H₄
Decane is cracked over a zeolite catalyst to give octane (a useful fuel) and ethene (a valuable alkene).
Thermal cracking uses temperatures up to .......... °C and pressures up to .......... atmospheres. It produces mainly .......... and alkanes. No catalyst is used.
Thermal cracking uses temperatures up to 1000 °C and pressures up to 70 atmospheres. It produces mainly alkenes and alkanes. No catalyst is used.
True or False?
Cracking produces only alkanes from longer-chain hydrocarbons.
False.
Cracking produces both smaller alkanes and one or more alkene molecules. For example, decane cracked to octane and ethene; ethene is an alkene.
Why is cracking commercially important?
Supply of long-chain fractions from crude oil exceeds demand, while shorter alkanes and alkenes are in high demand as fuels and as feedstocks for polymer production. Cracking converts surplus low-value fractions into higher-value products.
In catalytic cracking, a temperature of around .......... °C and a .......... catalyst are used. The main products are .......... and aromatic hydrocarbons.
In catalytic cracking, a temperature of around 500 °C and a zeolite catalyst are used. The main products are branched alkanes and aromatic hydrocarbons.
What is complete combustion of an alkane?
Complete combustion occurs when an alkane burns in excess oxygen. All carbon atoms are fully oxidised to carbon dioxide and all hydrogen atoms are oxidised to water. No carbon monoxide or soot is produced.
True or False?
Incomplete combustion of alkanes always produces carbon monoxide as the only carbon-containing product.
False.
Incomplete combustion produces carbon monoxide and/or carbon (soot) depending on how limited the oxygen supply is. Both can form alongside water.
.......... C₈H₁₈ + .......... O₂ → .......... CO₂ + .......... H₂O
2 C₈H₁₈ + 25 O₂ → 16 CO₂ + 18 H₂O
How does carbon monoxide harm the body?
Carbon monoxide binds strongly to haemoglobin in red blood cells, reducing its ability to carry oxygen. This can cause dizziness, unconsciousness, and in severe cases, death.
In a car engine, nitrogen reacts with oxygen at high temperature to form ........... This can be further oxidised in air to form ........... Both dissolve in water to form ........., contributing to acid rain.
In a car engine, nitrogen reacts with oxygen at high temperature to form NO (nitrogen monoxide). This can be further oxidised in air to form NO₂ (nitrogen dioxide). Both dissolve in water to form nitric acid, contributing to acid rain.
State two reactions that occur in a catalytic converter and write the equation for each.
1. Oxidation of CO: 2CO + O₂ → 2CO₂
2. Reduction of NO: 2CO + 2NO → 2CO₂ + N₂
Platinum, palladium, and rhodium on a ceramic honeycomb provide the catalytic surface.
True or False?
Flue gas desulfurisation using calcium carbonate produces calcium sulfate and carbon dioxide as products.
True.
CaCO₃ + SO₂ (g) + ½O₂ (g) → CaSO₄ (s) + CO₂ (g). The calcium sulfate (gypsum) produced is a useful by-product.
Incomplete combustion
Incomplete combustion occurs when an alkane burns in a limited supply of oxygen, producing carbon monoxide and/or carbon (soot) alongside water, rather than carbon dioxide.
Define free radical.
A tetrahedral molecule is a molecule with four bonding pairs of electrons around the central atom and no lone pairs, giving a bond angle of 109.5°. Examples include CH₄ and CCl₄.
In the initiation step of free-radical substitution, UV light causes .......... fission of the Cl–Cl bond, producing two .......... radicals.
In the initiation step of free-radical substitution, UV light causes homolytic fission of the Cl–Cl bond, producing two chlorine radicals.
True or False?
In the propagation step of free-radical substitution, the halogen radical is consumed and not regenerated.
False.
The halogen radical is regenerated in propagation, allowing a chain reaction to continue. A new alkyl radical attacks another halogen molecule to form a halogenoalkane and regenerate the halogen radical.
What are the three steps of free-radical substitution, in order?
1. Initiation
2. Propagation
3. Termination
The termination step occurs when two .......... collide and combine to form a single .......... molecule.
The termination step occurs when two free radicals collide and combine to form a single unreactive molecule.
True or False?
Free-radical substitution of alkanes with chlorine produces a single pure halogenoalkane product.
False.
A mixture of substitution products forms. If excess chlorine is present, multiple hydrogen atoms can be replaced, yielding a range of chlorinated compounds.
Define homolytic fission.
A trigonal planar molecule is a molecule with three bonding pairs and no lone pairs around the central atom, giving bond angles of 120° and a flat triangular shape. Examples include BF₃ and SO₃.
Why does the reaction between an alkane and chlorine require UV light?
UV light provides the energy needed for homolytic fission of the Cl–Cl bond to generate chlorine radicals in the initiation step. Without it, the alkane is too unreactive to react.

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