Why is carbon useful for making large compounds?
Because each carbon atom can make four strong bonds. Most commonly with other carbon atoms or hydrogen atoms.
What are hydrocarbons?
Any compound that is ONLY formed from carbon and hydrogen.
What are the first 5 alkANEs? (Monkeys Eat Purple Blueberries Politely)
Methane, Ethane, Propane, Butane, Pentane.
What is a homologous series?
(A group of organic compounds with the same general formula), similar chemical properties (so react in a similar way) and gradual variation in physical properties.
What is a key feature of alkanes (regarding their bonds)?
They are SATURATED COMPOUNDS.
- Every carbon atom has four single covalent bonds.
- There aren’t any double bonds.
What are trends as the length of carbon trend increases in alkanes?
Boiling point increases.
What state are the first four alkanes?
Shorter alkanes are usually gas at room temp.
What state are longer alkanes (5-17 carbon atoms)?
Liquid at room temp.
What state are really long chain alkanes (18+)?
Could be potentially solid at room temp.
What is a physical property of shorter alkanes?
More volatile- evaporate more easily due to really low boiling point.
More flammable- easier to ignite/ burn.
What is a physical property of longer alkanes?
More viscous- thick and sticky, honey like consistency.
What is a main use of hydrocarbons?
For fuel, as they release loads of energy when they’re burnt with oxygen.
Equation for complete combustion of hydrocarbons?
Hydrocarbon + oxygen —> CO2 + H2O
- hydrogen and carbon are each oxidised to form CO2 and H2O.
What type of reaction is the complete combustion of hydrocarbons?
Exothermic- lots of energy released.
Why are shorter hydrocarbons better fuels?
Because they are more volatile and flammable due to their low boiling points.
- Require less oxygen to burn completely - more efficient and cleaner.
What does the properties of hydrocarbons depend on?
Length of the carbon chains.
Are hydrocarbons a homologous series?
No. Alkanes and alkanes are.
What is crude oil?
- Fossil fuel.
- Get from deep underground.
- Mixture of lots of different compounds which nearly all of then are hydrocarbons (alkanes are more common).
How was crude oil formed?
- Remains of dead plants and animals mainly plankton.
- Animals dies millions of year ago and buried in the mud.
- High pressures and temperatures underground turned the organic biomass into crude oil.
why is crude oil considered finite?
Can’t be replenished on a human timescale as it takes a long time to form so if we continue to extract and use it at the current rapid rate it will run out.
Why do we separate the hydrocarbons in the mixture crude oil?
They each have different properties so well use them for different things.
Why does fractional distillation work for separating different compounds in crude oil?
Each of the compounds has a different boiling point.
Steps of fractional distillation of crude oil?
1)Feed oil into chamber and heat until most of it has turned into a gas.
2)Pass gaseous mixture into a fractionating column (hot at the bottom and cool at the top).
3) Gasses will rise up the column but condense into a liquid when they reach reigon with a lower temperature than their boiling point.
4) Longer chain hydrocarbons -> highest BP -> condense in the hotter regions near bottom of fractionating column.
5) Shorter chain -> lower BP -> condense in cooler regions near top.
6) Really shorter ones stay as a gas the entire time.
What are the uses of longer chain hydrocarbons (that are poor fuels)?
-Used for something else.
-Broken down into smaller hydrocarbons in cracking.
