Today, we will be talking about the chemical properties of Alkenes. Alkenes are part of homologous series with functional group of Carbon-Carbon double bonds.
When an alkene is burned in air
containing oxygen, carbon dioxide and water are formed as products. The general equation for this reaction is as follows:
Alkene + Oxygen → Carbon dioxide + Water
One such example is as follows:
Ethene + oxygen → 2CO + 2H2
Alkenes have greater amounts of carbon as compared to their corresponding alkanes, so it is possible that carbon particles might be produced upon combustion of alkenes. Thus, alkenes generally combust with a sootier glow than the alkanes which have the same amount of carbon atoms.Since alkenes have carbon-carbon single bonds in their structure, this makes them reactive and so they can be involved in addition reactions. These reactions can be demonstrated by simple equations. Today, we shall discuss 4 different addition reactions with an alkenes such as Ethene and Propene.
- Addition of bromine (aka bromination)
In general, the bromine solution has a reddish-brown color, but if we add an alkene to the bromine solution, the color of bromine solution rapidly disappears and thus, a colorless solution is being formed. This reaction is called Bromination. The equation for the reaction of propene and bromine is as follows:
How can be bromination be useful?
The reaction between the bromine and alkene is helpful in chemical tests. This reaction can be used as chemical test for the presence of unsaturated hydrocarbons. With the help of bromination, we can easily distinguish between an alkane and alkene. This is because alkane does not change color under ideal conditions as alkenes do.
- Addition of hydrogen(hydrogenation)
Alkenes can react with hydrogen gas in temperature of 200 C and catalyst such as the nickel, to form alkanes. This particular reaction is called hydrogenation.
In what ways can hydrogenation be helpful to us?
Hydrogenation plays an important role in the making of margarine. Edible oils (vegetable oils) contain carbon=carbon bonds. When these oils go through the hydrogenation process, they are eventually converted into margarine.
- Addition hydration (adding steam)
The reaction of alkene with steam can form alcohols. The required conditions for this reaction to take place are a temperature of 300C and a pressure of about 60 atmospheres. This reaction also requires a catalyst such as Phosphoric(V) acid, H3PO4.
In the presence of suitable catalysts and also at high pressure and temperature, the ethene molecules can react with other ethene molecules to form a very long macromolecule called poly(ethene). This process is known as addition polymerization. The equation for this reaction can be written as follows:
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