What are the general formulae for alkenes?

The general formula for alkenes is CnH2n.

Alkenes are a type of hydrocarbon, which means they are made up of hydrogen and carbon atoms. The general formula for alkenes is CnH2n. This formula indicates that for every n number of carbon atoms, there are twice as many hydrogen atoms. For example, if n is 2, the formula would be C2H4, which is the formula for ethene, the simplest alkene.

The 'n' in the formula represents the number of carbon atoms in the molecule. This can be any whole number starting from 2. The '2n' represents the number of hydrogen atoms, which is always double the number of carbon atoms. This is because each carbon atom can form four bonds and in alkenes, one of these bonds is a double bond between two carbon atoms, leaving the remaining bonds for hydrogen atoms.

Alkenes are unsaturated hydrocarbons, which means they contain a carbon-carbon double bond. This double bond gives alkenes their characteristic chemical properties, such as the ability to undergo addition reactions. In these reactions, the double bond breaks and new atoms are added to the carbon atoms.

The general formula CnH2n is a useful tool for predicting the molecular formula of an alkene when you know the number of carbon atoms. It also helps to understand the structure and properties of alkenes. For instance, as the number of carbon atoms increases, the physical properties of the alkene change, such as its boiling point and solubility.