Organic chemistry

• Define hydrocarbon.

  A compound made of only hydrogen and carbon atoms.
• Hydrocarbons have how many carbon bond?

  4 these can be doubly or single bonds but cannot have more than 4 at a time.
• Define homologous series.

  A group of molecules with similar properties and share a general formula.
• What are the two hydrocarbon homologous series?

  Alkanes and Alkenes.
• What kind of bonds do alkanes have?

  Single bonds (saturated)
• What are the first 4 alk(anes)/alk(enes)?

  Meth - 1 Carbon atom

  Eth - 2 Carbon atoms

  Prop - 3 Carbon atoms

  But - 4 Carbon atoms
• What’s the general alkane formula?

  C(n)H(2n+2)
• State some properties of alkanes.

  They have an inability to miss with water.

  Low boiling points and flammability.
• How are the properties of an alkane influenced?

  By the length of the alkane chain.
• Alkanes have 3 important trends, one being their boiling and melting point. Explain this trend.

  As the length of the chain increases, the melting and boiling point both increase. This is because they have more intermolecular forces when longer increases their strength so much more energy is required to break these bonds.
• State a trend alkanes have.

  Flammability decreases when the chain length increases.
• Explain alkanes correlation with viscosity.

  The viscosity of an alkane increases as the chain length increases because the attraction between the chains increase when the chain length increases. This makes it more difficult for the chains to move over one another and spread out making it more thick and less mobile when liquid.
• Define viscosity.

  Viscosity refers to the thickness and resistance of a liquid.
• Define volatile.

  How easily a substance evaporates.
• Define combustion.

  To burn in oxygen.
• When combusted, describe an alkanes change in energy.

  The process is highly exothermic so they release a lot of energy and are commonly burned to produce heat or as fuels. The released energy often comes from the hydrogen-oxygen and carbon-oxygen bonds being formed. The longer the alkane the more energy released.
• Define incomplete combustion.

  When not enough oxygen is presebt to oxidise all the atoms of hydrocarbon.
• What’s the equation for complete combustion with Hydrocarbons?

  Hydrocarbon + Excess Oxygen —> Carbon Dioxide + Water

  or

  ?C?H? + ?O2 —> ?CO2 + ?H2O

  (question marks change depending on which hydrocarbon is burnt)
• What’s the general formula for alkenes?

  CnH2n
• What kind of bonds do alkenes have?

  Double bonds (unsaturated).
• Which homologous series is more likely to form complete combustion?

  Alkanes.
• what is the formula for incomplete combustion with hydrocarbons?

  Hydrocarbon + Oxygen —> carbon monoxide + carbon (soot) + water

  or

  ?H?C? + ?O2 —> ?CO + ?C + ?H2O
• What are fossil fuels?

  Non-renewable energy sources formed from the remains of ancient plants and animals.
• How is crude oil formed?

  Crude oil is formed from the remains of ancient marine plants and animals that were buried and subjected to heat and pressure over millions of years. The pressure caused the organic compounds made up of these organisms to liquify.
• How long does crude oil take to form?

  Millions of years. However we use it at a much faster rate than it can be replaced.
• What is crude oil?

  Crude oil is a mixture of hydrocarbon compounds that vary in size.
• What is crude oil also known as?

  feedstock.
• On its own crude oil is fairly useless but when split it’s used for two things. What are these?

  Fuel and petrochemicals
• What kind of fuels do crude oils contain?

  Kerosene - jet fuel

  petrol and diesel- used to power cars

  heavy fuel oil - used in shipping and power stations
• Crude oil is a source of starting materials. give some examples.


  petrochemicals such as

  solvents

  lubricabrs

  detergents

  polymers
• How are hydrocarbons extracted from crude oil?

  fractional distillation.
• What’s a fraction?

  A group with crude oil separated according to the hydrocarbons boiling point.
• Fractional distillation

  1. Crude oil passes through a furnace heated up to around 350C

  2. Hydrocarbon compounds in the crude oil evaporate

  3. Mixture of gaseous hydrocarbon is fed into a distillation column

  4. Gas travels up the column and cools and condenses

  5. Compounds with similar boiling points evaporate at similar heights forming fractions

  6. Fractions are condensed and collected to be used as fuels
• What is cracking?

  a chemical process using thermal decomposition to break apart individual molecules.
• How do cracking and fractional distillation differ?

  Fractional distillation takes advantage of the physical properties of the different molecules whereas cracking just uses thermal decomposition. cracking is done to produce shorter more useful chain alkanes from longer less useful ones where’s as fraction distillation is just the the step before that separated them.
• What is produced from cracking?

  A long chain alkane —> short chain alkene + short chain alkane
• What are the 2 types of cracking?

  catalytic cracking and steam cracking.
• What is catalytic cracking?

  Process of breaking down large hydrocarbon molecules into smaller ones using a catalyst; long chain hydrocarbons are first heated and vapour used. The vapour is passed over a hot powdered aluminium oxide catalyst. the long chain molecules will break apart on the catalysts surface producing both shorter alkanes and alkenes.
• What is steam cracking?

  Process of breaking down hydrocarbon molecules in the presence of steam to produce smaller molecules; a long chain alkane is heated and vapour used then mixed with steam. Its then heated to a higher temperature breaking down into shorter alkanes and alkenes