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Hydrocarbons Flashcards

1
Q

What are hydrocarbons?

A

Hydrocarbons are organic compounds made of hydrogen and carbon atoms.

Hydrocarbons are the simplest organic compounds.

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2
Q

What is the general formula for alkanes?

A

The general formula for alkanes is CnH2n+2.

Alkanes are saturated hydrocarbons.

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3
Q

List the first four alkanes.

A
  • Methane: CH4
  • Ethane: C2H6
  • Propane: C3H8
  • Butane: C4H10

These are the simplest alkanes.

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4
Q

What defines alkanes?

A

Alkanes have all C-C single bonds and are saturated compounds.

Each carbon atom in alkanes forms four single covalent bonds.

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5
Q

How do hydrocarbon properties change with carbon chain length?

A
  • Shorter carbon chains are less viscous
  • Shorter carbon chains are more volatile
  • Shorter carbon chains are more flammable

These properties influence their uses as fuels.

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6
Q

What occurs during complete combustion of hydrocarbons?

A

Complete combustion produces carbon dioxide and water vapor, releasing energy.

The reaction is: hydrocarbon + oxygen → carbon dioxide + water (+ energy).

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7
Q

What is oxidation in the context of hydrocarbons?

A

Oxidation is defined as the gain of oxygen.

During combustion, both carbon and hydrogen from hydrocarbons are oxidized.

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8
Q

What is the balanced equation for the complete combustion of methane (CH4)?

A

CH4 + 2O2 → CO2 + 2H2O.

This equation balances the number of atoms on both sides.

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9
Q

What is the relationship between carbon chain length and viscosity?

A

As carbon chain length decreases, viscosity decreases (more runny).

Shorter hydrocarbons are less gloopy.

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10
Q

Fill in the blank: The shorter the carbon chain, the more _______ a hydrocarbon is.

A

flammable.

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11
Q

True or False: Hydrocarbons are used as fuels due to the low energy released during combustion.

A

False.

Hydrocarbons release a lot of energy when combusted completely.

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12
Q

What is a displayed formula in the context of hydrocarbons?

A

A displayed formula shows all the atoms and bonds in a molecule.

It visually represents the structure of the hydrocarbon.

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13
Q

How does flammability change with carbon chain length?

A

Shorter carbon chains are more flammable (easier to ignite).

This affects their practical applications as fuels.

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14
Q

What is crude oil formed from?

A

The remains of marine organisms, mainly plankton, buried under sediment over millions of years.

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15
Q

Why are fossil fuels considered non-renewable?

A

They take millions of years to form, and we are using them faster than they can be replenished.

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16
Q

What is fractional distillation?

A

A process used to separate different hydrocarbon fractions in crude oil based on their boiling points.

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17
Q

Define hydrocarbons.

A

Molecules containing only hydrogen and carbon.

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18
Q

What happens to crude oil during fractional distillation?

A

It is heated to convert most of it into gas, which is then separated in a fractionating column.

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19
Q

Describe the temperature gradient in a fractionating column.

A

It is hot at the bottom and gets cooler as you go up.

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20
Q

What happens to longer hydrocarbons during fractional distillation?

A

They have high boiling points, condense back into liquids, and drain out early near the bottom of the column.

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21
Q

What is LPG primarily composed of?

A

Propane and butane.

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22
Q

Where does petrol drain in a fractionating column compared to diesel?

A

Petrol drains further up the column than diesel, indicating it has a lower boiling point.

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23
Q

List the fractions obtained from crude oil in order of increasing boiling point.

A
  • LPG
  • Petrol
  • Kerosene
  • Diesel oil
  • Heavy fuel oil
  • Bitumen
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24
Q

True or False: Crude oil is a finite resource.

A

True.

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25
Q

Fill in the blank: Hydrocarbons are molecules containing only ______ and ______.

A

hydrogen, carbon

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26
Q

What is the significance of the boiling points of hydrocarbons in fractional distillation?

A

They determine where in the column the hydrocarbons will condense and drain out.

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27
Q

What does the term ‘fraction’ refer to in the context of fractional distillation?

A

A mixture of hydrocarbons that contain a similar number of carbon atoms.

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28
Q

What are some important products derived from crude oil?

A
  • Fuel oil
  • Liquid petroleum gas (LP)
  • Polymers
  • Solvents
  • Lubricants
  • Detergents

These products are examples of organic compounds that come from crude oil.

29
Q

What are homologous series?

A

Groups of similar compounds with many properties in common

Examples include alkanes and alkenes.

30
Q

What is the purpose of cracking in petroleum processing?

A

To split long-chain hydrocarbons into shorter, more useful ones

Short-chain hydrocarbons are more flammable and in high demand.

31
Q

What type of hydrocarbons does cracking produce?

A
  • Alkanes
  • Alkenes

Alkenes are used as starting materials for making other compounds and polymers.

32
Q

What is the process of catalytic cracking?

A

Vaporizing long-chain hydrocarbons and passing them over a hot powdered aluminium oxide catalyst

This process splits the long-chain molecules on the surface of the catalyst.

33
Q

What is steam cracking?

A

Vaporizing hydrocarbons, mixing them with steam, and then heating to a very high temperature

This method is another way to crack hydrocarbons.

34
Q

Fill in the blank: Cracking is a thermal _______ reaction.

A

decomposition

35
Q

What must be balanced in chemical equations for cracking?

A

The number of carbon and hydrogen atoms on both sides of the equation

This ensures the law of conservation of mass is followed.

36
Q

What are the examples of long-chain hydrocarbons mentioned?

A
  • Decane (ten C atoms)
  • Octane (eight C atoms)

These examples illustrate the types of hydrocarbons that can be cracked.

37
Q

True or False: Short-chain hydrocarbons are less useful than long-chain hydrocarbons.

A

False

38
Q

What are some important products derived from crude oil?

A
  • Fuel oil
  • Liquid petroleum gas (LP)
  • Polymers
  • Solvents
  • Lubricants
  • Detergents

These products are examples of organic compounds that come from crude oil.

39
Q

What are homologous series?

A

Groups of similar compounds with many properties in common

Examples include alkanes and alkenes.

40
Q

What is the purpose of cracking in petroleum processing?

A

To split long-chain hydrocarbons into shorter, more useful ones

Short-chain hydrocarbons are more flammable and in high demand.

41
Q

What type of hydrocarbons does cracking produce?

A
  • Alkanes
  • Alkenes

Alkenes are used as starting materials for making other compounds and polymers.

42
Q

What is the process of catalytic cracking?

A

Vaporizing long-chain hydrocarbons and passing them over a hot powdered aluminium oxide catalyst

This process splits the long-chain molecules on the surface of the catalyst.

43
Q

What is steam cracking?

A

Vaporizing hydrocarbons, mixing them with steam, and then heating to a very high temperature

This method is another way to crack hydrocarbons.

44
Q

Fill in the blank: Cracking is a thermal _______ reaction.

A

decomposition

45
Q

What must be balanced in chemical equations for cracking?

A

The number of carbon and hydrogen atoms on both sides of the equation

This ensures the law of conservation of mass is followed.

46
Q

What are the examples of long-chain hydrocarbons mentioned?

A
  • Decane (ten C atoms)
  • Octane (eight C atoms)

These examples illustrate the types of hydrocarbons that can be cracked.

47
Q

True or False: Short-chain hydrocarbons are less useful than long-chain hydrocarbons.

A

False

48
Q

What are alkenes?

A

Alkenes are unsaturated hydrocarbons that contain a C=C double bond

They are distinct from alkanes, which do not have double bonds.

49
Q

What does the C=C double bond in alkenes indicate?

A

Alkenes have two fewer hydrogens compared to alkanes with the same number of carbon atoms

This unsaturation makes them reactive.

50
Q

List the first four alkenes.

A
  • Ethene
  • Propene
  • Butene
  • Pentene

Each alkene has a corresponding number of carbon atoms.

51
Q

What is the general formula for alkenes?

A

CₙH₂ₙ

This indicates that for every carbon atom, there are twice as many hydrogen atoms.

52
Q

How do alkenes burn in the presence of oxygen?

A

Alkenes can combust completely to produce water and carbon dioxide, but often undergo incomplete combustion

Incomplete combustion produces carbon and carbon monoxide.

53
Q

What is produced during incomplete combustion of alkenes that is not produced during complete combustion?

A
  • Carbon
  • Carbon monoxide (CO)

Incomplete combustion occurs due to insufficient oxygen.

54
Q

What is the color of the flame produced by incomplete combustion of alkenes?

A

Smoky yellow flame

This is due to the production of carbon particles.

55
Q

True or False: Alkenes have a C=C bond.

A

True

This differentiates them from alkanes, which have only single bonds.

56
Q

Fill in the blank: The alkene with the chemical formula C₈H₁₄ contains _______ carbon atoms.

A

eight

57
Q

What happens to the double bond in alkenes during a reaction?

A

The C=C double bond can open up to form single bonds, allowing bonding with other atoms

This increases their reactivity.

58
Q

Provide an example of an equation for incomplete combustion of an alkene.

A

C₈H₁₄ + O₂ → 2C + 2CO + 4H₂O

The specific products may vary based on oxygen availability.

59
Q

What type of reactions do alkenes primarily undergo?

A

Addition reactions

Alkenes react most of the time via addition reactions, where the carbon-carbon double bond opens to form a single bond and new atoms are added.

60
Q

What is hydrogenation?

A

The addition of hydrogen to an alkene

Hydrogenation involves reacting an alkene with hydrogen in the presence of a catalyst to form a saturated alkane.

61
Q

What characterizes alkenes as a homologous series?

A

Same functional group and similar reactions

Alkenes are a homologous series because they all share the same functional group, leading to similar chemical behavior.

62
Q

What product is formed when alkenes react with steam?

A

Alcohols

When alkenes react with steam, water is added across the double bond to form alcohols.

63
Q

How is ethanol industrially produced from ethene?

A

By mixing ethene with steam and passing it over a catalyst

The reaction mixture is then condensed, allowing for the separation of ethanol and water from unreacted ethene.

64
Q

What happens to the boiling points of ethanol and water compared to ethene?

A

Ethanol and water have higher boiling points than ethene

This property allows for the condensation and subsequent purification of ethanol from the reaction mixture.

65
Q

What type of compounds do alkenes form when they react with halogens?

A

Saturated compounds

The addition of halogens such as bromine or chlorine to alkenes results in saturated compounds.

66
Q

What is the reaction of bromine with ethene called?

A

Dibromoethane formation

The reaction between ethene and bromine produces dibromoethane, as two bromine atoms are added.

67
Q

What indicates a reaction has occurred when bromine water is added to an alkene?

A

The bromine water becomes colourless

The decolourisation of orange bromine water indicates that the alkene has reacted, forming a colourless dibromo-compound.

68
Q

When bromine water is added to a saturated compound, what is the expected observation?

A

The solution remains bright orange

No reaction occurs with saturated compounds like alkanes, thus the colour remains unchanged.

69
Q

Fill in the blank: The presence of a _______ catalyst at 60 °C is necessary for hydrogenation.

A

nickel

Nickel is commonly used as a catalyst in the hydrogenation of alkenes.

Hydrocarbons (1 decks)

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