Alkanes are the simplest organic compounds. They consist of a chain of carbons bonded together by single bonds. They are saturated hydrocarbons. For example: CH₃-CH₃ (ethane)
Alkenes are similar but they have at least one carbon-carbon double bond. They are unsaturated hydrocarbons. For example: CH₂=CH₂ (ethene)
Since alkanes are saturated (only single bonds) they have stronger intermolecular forces, and we need a lot of energy to break their bonds. They are less reactive. In other hand, we have the unsaturated alkenes that have the double bond and are easier to break. They are more reactive.