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Chemistry > C9 - Hydrocarbons > Flashcards

C9 - Hydrocarbons Flashcards

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1
Q

How is crude oil formed and where is it found

A

It is found in rocks
It is formed over millions of years when the remains of sea plants and animals than contained carbon dioxide got buried under rocks in high pressure and temperature conditions

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2
Q

What is crude oil made of

Chemistry wise

A
  • A mixture of compounds, mainly hydrocarbons
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3
Q

What are the first four alkanes

A

Methane, Ethane, Propane and Butane

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4
Q

What is a hydrocarbon

A

Molecules made up of hydrogen and carbon atoms only

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5
Q

General formula for alkanes

A

CnH2n+2

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6
Q

What are alkanes

A

A homologous series of saturated hydrocarbons where the bonds between all atoms are single covalent bonds. Each carbon atom bonds to 4 other atoms

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7
Q

Properties of hydrocarbons and what they mean

A
  • Viscosity - thickness of the fluid (how easily it flows)
  • Flammability - how easily it combusts
  • Volatility - the tendency to turn into a gas
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8
Q

How does the size of a hydrocarbon relate to its properties

A
  • Viscosity - as the size of the hydrocarbon increases, the viscosity increases - long chain hydrocarbons are extremely viscous
  • Flammability - the shorter the hydrocarbon chain, the more flammable the hydrocarbon is and the cleaner (less smoky) the flame is
  • Volatility - As the hydrocarbon chain size increases, the boiling point increases meaning the larger hydrocarbons are less volatile
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9
Q

What happens when hydrocarbon fuels are combusted

Complete combustion

A
  • They release energy to their surroundings (exothermic) when combusted
  • The carbon and hydrogen atoms are oxidised to produce carbon dioxide and water (complete combustion)
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10
Q

Equation for the complete combustion of a hydrocarbon e.g. methane

A

CH4 + 2O2 —> CO2 + 2H2O

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11
Q

How is crude oil separated and what does this process form

A
  • Through fractional distillation
  • This process forms separate fractions which are groups of hydrocarbons with similar numbers of carbon atoms
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12
Q

Stages of industrial fractional distillation

A
  1. Crude oil is heated to a very high temperature so it evaporates
  2. The crude oil vapour is then pumped into the bottom of the fractionating column which is hotter at the bottom and cooler at the top
  3. The vapors rise up the column and condense when they reach their boiling points - this repeats for all remaining hydrocarbons
  4. The liquid fractions are then removed
  • The long chain hydrocarbons have high boiling points son they condense and are removed from the bottom
  • The shorter chain ones habve low boiling points and some remain as gases and are collected from the top where the temperature is lower
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13
Q

What does incomplete combustion produce

A
  • Carbon monoxide
  • This is a toxic, colourless and odourless gas
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14
Q

Uses of common fractions of crude oil

A
  • Petrol and diesel - fuels for cars
  • Kerosene - jet fuel
  • Liqified petroleum gases - camping stoves, gas cylinders
  • Heavy fuel oil - ships
  • Bitumen - roads
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15
Q

How are fractions used in the petrochemical industry

A

They are uses as feedstock - this means they are used to create other chemicals
These new chemicals can include solvents, lubricants, detergents and polymers

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16
Q

What is cracking and name the two types

A

The breaking down of a long chain hydrocarbon into a smaller, more useful and higher in demand hydrocarbons
It is a thermal decomposition reaction
The two types are catalytic cracking and steam cracking

17
Q

Conditions for catalytic cracking

A
  • High temperature
  • A catalyst e.g. aluminium oxide or porous pot
18
Q

Conditions needed for steam cracking

A
  • High temperature
  • Vaporised hydrocarbons are combined with steam
19
Q

Properties and use of alkanes

A
  • Low reactivity
  • Combust easily
  • Therefore they are used as fuels
20
Q

Test for unsaturation

A
  • Add bromine water
  • If a molecule with a carbon-carbon double bond is used e.g. an alkene which is unsaturated, thte bromine water turns from orange to colourless because the alkene reacts with the bromine (forms 1,2 -dibromoethane)
21
Q

Properties that make a good fuel

A
  • Flammable
  • High volatility
  • Low boiling point
  • This is why shorter chain alkenes are very good fuels

Chemistry (17 decks)

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