Organic Chemistry - Definitions
General Formula - An algebraic formula that can describe any member of a family of compounds (i.e. CnH2n+2)
Empirical Formula - Simplest ratio of atoms of each element in a compound (i.e. C2H5)
Molecular Formula - The actual number of atoms of each element in a molecule, with functional groups indicated. (i.e. C4H10)
Structural Formula - Shows the atoms Carbon by Carbon, with the attached Hydrogens and functional groups. (i.e. CH3CH2CH2CH3)
Displayed Formula - Shows how the atoms are arranged and the bonds between them.
Homologous Series - Bunch of organic compounds with the same general formula.
Structural Isomer - Same molecular formula; atoms connected in different ways.
Chain Isomers - Different arrangement of the Carbon skeleton.
Positional Isomers - Same skeleton and same atoms/groups of atoms attached but it is attached to a different Carbon.
Functional Group - Same atoms arranged into different functional groups.
Organic Chemistry - Alkanes and Petroleum
- Alkanes are hydrocarbons with the general formula CnH2n+2 and are saturated.
- Crude Oil (petroleum) is mainly alkanes and can be separated into fractions by fractional distillation:
1) Crude oil is vaporised at 350c.
2) Vaporised crude oil goes into a fractionating column and rises through the trays. Large Hydrocarbons won't vaporise.
3) As the vapour goes up the column it gets cooler. Each fraction condenses at a different temperature and are drawn off at different levels. [340c = Mineral oil;
250c = Gas Oil (diesel); 180c = Kerosene/paraffin (Jet Fuel/Central Heating);
110c = Naphtha (Petrochemicals); 40c = Petrol]
4) The Hydrocarbons with the lowest boiling points don't condense and are drawn off as gases at the top.
Organic - Petroleum + Alkanes as Fuels
- Heavy fractions can be cracked to make smaller molecules which are in high demand and more valuable, i.e. C10H22 > C2H4 + C8H18
Thermal Cracking - Takes place at high temperatures and high pressure; Produces lots of alkenes; Alkenes used to make valuable products like polymers.
Catalytic Cracking - Makes motor fuels and aromatic hydrocarbons; Uses a Zeolite catalyst (hydrated aluminosilicate) at a slight pressure and high temperature; Cheaper, and catalyst speeds up the reaction.
- Combustion burns alkanes with O2 to produce CO2 and H2O.
- Incomplete combustion (not enough O2) produces CO which is poisonous as it binds to sites on Haemoglobin. CO can be removed by catalytic converters.
- NOx are produced when high pressure and temperature in car engines cause N2+O2 in air to react. The hydrocarbons + NOx react in sunlight to form ground-level Ozone which contributes to smog, irritates peoples eyes, aggravates respiratory system and causes lung damage.
Organic - Alkanes as Fuels
- Catalytic converters remove unburnt hydrocarbons and NOx's.
- Acid rain is caused by burning fossil fuels that contain Sulfur. The Sulfur burns to produce SO2 which enters the atmosphere and is converted to H2SO4.
- Acid rain destroys trees and vegetation but SO2 can be removed using CaO.
- Greenhouse gases stop heat from the Sun going back into space. CO2 is a green house gas and burning fossil fuels produces CO2.
- Some electromagnetic radiation from the Sun reaches the Earth and is absorbed. The Earth then re-emits it as infrared radiation.
- 3 Main greenhouse gases are Water Vapour, CO2 and CH4. Too much heat is getting trapped and the Earth is getting warmer (Global Warming).
- When alkanes in fossil fuels are burned they also produce Water Vapour.
- Methane is produced by rubbish rotting in landfill sites.