All carbon compounds show some common characteristic properties. Four important chemical reactions are discussed below: Combustion Reactions:When Carbon and its compounds burn in the presence of Oxygen (or air), they give CO2, heat and light.The process of burning carbon and its compounds in excess of oxygen for the release of heat and light (energy) is know as combustion.Following are some of the examples of combustion reaction of organic compounds:C + O2 ? CO2 + Heat + LightC3H8 + 5O2 = 3CO2 + 4H2O.+ Heat + Light(C3H8 is the molecular formula for Propane, a common gas present in LPG which we burn for cooking in our kitchens).In General, saturated hydrocarbons burn with a clear blue flame, whereas unsaturated hydrocarbons burn with a yellow flame producing soot (carbon).Combustion of hydrocarbons may be of two types: Complete combustion and incomplete combustion.Complete combustion of hydrocarbons occurs in excess of oxygen(air), producing CO2 and H2O as the only final chemical products.Heat and light (clear blue flame) as a form of energy is generated.Incomplete combustion occurs when there is insufficient Oxygen(air) and the hydrocarbon is in excess.This reaction burns with a sooty or smokey flame and produces products which are CO(g) and/or C(s) and H2O.Oxidation Reactions:In an combustion reaction, carbon compounds are oxidized in the presence of oxygen. Though combustion is generally an oxidation reaction, not all oxidation reactions are combustion reactions. Oxidation is also carried out by using oxidizing agents (Oxidants) .Oxidizing agents, also referred as Oxidants are substances that oxidize other substances, while undergoing reduction themselves.Alcohols undergo oxidation in presence of Oxidants like alkaline potassium permanganate (KMnO4) to form carbolic acids.For Example: Ethanol undergoes oxidation to produce Acetic acid , when heated with an Oxidizing agent like alkaline KMnO4.Addition reactions:Unsaturated organic compounds , like alkenes and alkynes, contain multiple bonds (C=C ,C?C) between their carbon atoms.They undergo addition reactions to become saturated in nature.The formation of larger molecules by addition of more radicals is known as addition reaction.During an addition reaction of unsaturated organic compounds, a reagent takes place at the double bonded or triple bonded carbon atoms.For example; ethene is converted into ethane when heated with the catalyst nickel.CH2=CH2 + H2 + (Nickel catalyst) ? CH3?CH3Nickel acts as a catalyst, which basically regulates (increase/decrease) the rate of a given reaction, without itself undergoing any chemical change.When ethene undergoes addition reaction with chlorine, it gives dichloroethane.Chlorine is a halogen, whose atoms partially break the carbon-carbon double bond in the alkene to a single bond and add itself across it.Substitution Reaction:Substitution reaction is one in which an atom or a group of atoms(functional group) in the compound are replaced by another atom (or group of atoms). Substitution reactions are single displacement reactions.Alkanes, which have only single bonds between their carbon atoms, are saturated hydrocarbons.They are chemically least reactive.They are also called paraffins, as they have no affinity (minimum affinity)towards chemical changes (parum=little ;affins=affinity).However, under suitable conditions they undergo substitution reactions.For example, under the presence of Sunlight, Methane reacts with chlorine gas to produce chloromethane and hydrogen chloride.CH4 + Cl2 + Sunlight ? CH3Cl + HClSunlight (UV Light) breaks down the chlorine into free radicles, which initiates the substitution reaction.