C9

An example of cracking

Decane c10H22 is a medium sized alkane molecule. When it is heated to 500 with a catalyst it breaks down. One for the molecules is produces in pentane C5H12 which is used petrol. Propene and ethene are also made, which the chemical industry can use to produce polymers and other chemicals such as solvents. Decane > pentane + propene + ethene. This cracking is a reaction is an example od thermal decomposition. Notice how cracking produces different types of molecules. One of the molecules is pentane. The first part if its name tells us that it ad five carbon atoms. The last part if its name shows that it is an alkane. Pentane is a saturated hydrocarbon, its molecules have as much hydrogen as much as possible in them. The other molecules in this reaction have names that end slightly differently. They end in ene. We call this type of molecule an alkene. The different end in -ene tell us that these molecules are unsaturated. Unsaturated compounds contain at least one double bond between their carbon atoms. You can see that these alkenes have one double covalent bond in their molecules. As carbon atoms form four covalent bonds, it means that the unsaturated alkene molecules have two fewer hydrogen atoms in their modules than the started alkane molecules with the same number of carbon atoms. Tests on the gaseous products form the experiment above show that alkanes burn in the air (but not as well as equivalent small alkanes witches are used as fuels) react with bromine water which is orange in colour, decolorizing it. Alkanes are genially more reactive than alkanes. The reaction with bromine water is used as a test to see if an organic compound is unsaturated. A positive test for an unsaturated hydrocarbon is that it turns orange bromine water colourless. The alkanes do not react with bromine water, so you can use this test to distinguish between an alkene and an alkane.

Incomplete combustion

all fossil fuels (oil, coal and natural gas) produce carbon dioxide and water when they burn in plenty of air. When there is not enough oxygen there is incomplete combustion. Instead of carbon dioxide forming, carbon monoxide is formed, this is a toxic gas. It is colourless and odourless. Your red blood cells pick up this gas and carry it around your body instead of oxygen.

Crude oils

crude oil is finite resources found in rocks. It was formed over millions of years from the remains of sea animas and plants, mainly plankton that were buried in the mud. Over time, layer upon layer if rock was laid down on top, creating the conditions (high presser and temp, in the abbsens of oil) to make crude oil. The crude oil forms I a dark, smelly liquid It is a mixture of many different carbon compounds, A mixture contains two or more elements or compounds that are not chemically combined, nearly all the compounds in crude oil are compounds containing only hydrogen and carbon atoms. These are hydrocarbons. Crude oil from the ground is nor useful as there are too many substances in to, all with different boiling points. Before crude oil can be used it mused be separated into different substances with similar boiling points. These are known as fractions. The properties of substances do not change when they are missed the mixtures or substances in crude oil can be separated in the lab by distillation. Distillation separates liquids with different boiling points.

Fractional distillation of crud oil

crude oil is separated into hydrocarbons with similar boiling points, called fractions. This is fractional distillation. Each hydrocarbon creation contains molecules with similar numbers d carbon atoms. Each of these fractions boil at different tempter ranges because of the different sixed of the molecules in it. Crude oil is heated in the bottom of a tall rower (fractionating column) as hot vapour. The column is kept very hot at the bottom and much cooler at the top, so the temp decreases going up the column. The gases more up the column and they hydrocarbons condense when they reach the temperature of their boiling points. The different fractions are collected as liquids at different levels. The fractions are collected from the column I a continuous process. Hydrocarbons with the smallest molecules have the lowest boiling points. They are piped out of the cooler top of the column as gases. At the bottom of the column, the fractions had high boiling points. They cool to form very think liquids or solids at room temp. once collected the fractions need more processes before they can be used.

Alkanes

most of the hydrocarbons in crude oil are alkanes. The first part of the name of each alkane tells you how many carbon atoms are in its molecules. You describe alkanes as substrate hydrocarbons. All the carbon carbon bonds are single covalent bonds. This means they contain as many hydrogen atoms as possible in each molecule. No more hydrogen atoms can be added.

What crack hydrocarbons?

some of the heavier fractions from the fractional distillation od crude oil are not in high demand. The hydrocarbons in them are made up of large molecules. They are think liquids or solids with high bowling points. They are difficult to vaporise and do not burn easily, so they are pure fuels, although they do have their uses. Yet the main demand from crud oil id for fuels and starting metals for the chemical industry. The largest less useful hydrocarbon molecules can be broken down into smaller, more useful once in cracking. The process takes place at an oil refinery in steel vessels called crackers. In the cracker, a heavy fractional distillation from crude oil is heated to vaporise the hydrocarbons. The vapor is passed over a hot catalyst of mixed with steam and heated to a very high temp. the hydrocarbons are cracked so thermal decomposition reactions take place. The large molecules spilt apart to form smaller more useful ones.

Complete combustion

the lighter fractions from crude oil are very useful as fuels. When hydrocarbons urn in plenty of air they transfer lots of energy to the surroundings. For example, propane + oxygen > carbon dioxide + water. The carbon and hydrogen in the fuel are oxidised completely when they burn like this. Oxidation means adding oxygen in a chemical reaction. The producers of the complete combustion of a hydrocarbon are carbon dioxide and water.

The properties of hydrocarbons

there is a great verity of hydrocarbon molecules. Short chain molecules that make up hydrocarbons tend to be the most useful. They make good fuels as they ignite easily and burn well, with less smoky flames and hydrocarbons made up of large molecules. They are very flammable. Other hydrocarbon has lots of carbon atoms in their ling chain molecules, and may have since chains or form rings.