Unit 3: Section 2 - Alkanes and Halogenoalkanes Flashcards
Define a hydrocarbon.
A molecule made from only carbon and hydrogen atoms.
What are alkanes?
Saturated hydrocarbons
Define saturated.
Saturated means all the possible bonds from an atom are being used
What is crude oil made up of?
Hydrocarbons - mostly alkanes
Describe and explain the process of fractional distillation. (4)
- The crude oil is vapourised at about 350 degrees.
- The vaporised crude oil goes into a fractionating column and rises up through the trays. The largest hydrocarbons don’t vaporise at all, because their boiling points are too high - they run to the bottom to form a gooey residue.
- As the crude oil vapour goes up the fractionating column, it gets cooler. Because the alkane molecules have different chain lengths, they have different boiling points, so each fraction condenses at a different temperature. The fractions are drawn off at different levels of the fractionating column.
- The hydrocarbons with the lowest boiling points don’t condense. They’re drawn off as gas at the top of the column.
Define cracking.
The process of breaking long-chain hydrocarbons into short-chained hydrocarbons.
Describe the two methods of cracking.
Thermal cracking:
- – Takes place at high temperature (up to 1000 degrees) and high pressure (up to 70 atm)
- – It produced a lot of alkenes.
Catalytic cracking
- – This uses a zeolite catalyst at a slight pressure and high temperature (450 degrees).
- – Mostly produces aromatic hydrocarbons and motor fuels.
What are the products of complete combustion?
Water and carbon dioxide
What are the products of incomplete combustion?
Carbon monoxide as well as of instead of carbon dioxide.
Soot (Carbon) instead of carbon dioxide.
How do greenhouse gases contribute to global warming?
Greenhouse gases are good at absorbing infrared energy. They emit some of the energy they absorb back towards the Earth, keeping it warm.
What causes smog? (2) How are these things made?
Unburnt hydrocarbons - from engines that don’t burn all of their fuel molecules.
Oxides or nitrogen - these are produced when the high pressure and temperature in a car engine causes the nitrogen and oxygen atoms in the air to react together.
What causes acid rain?
Some fossil fuels contain sulphur impurities and when they are burnt they release sulphur dioxide gas. If the sulphur dioxide gets into the atmosphere it dissolves in the moisture and it converted into sulphuric acid. This then falls as acid rain.
How do we remove impurities from power station flue gases before they get into the atmosphere?
Powdered calcium carbonate or calcium oxide is mixed with water to make alkaline slurry. This is mixed with the flue gases and the impurities react to make harmless compounds.
What is a free radical?
A highly reactive particle with an unpaired electron.
How do free radicals form?
When a covalent bond splits equally, giving one electron to each atom
