The burning of fuel releases energy mainly as heat.
Coal is a complex mixture of compounds of carbon, hydrogen and oxygen, and some free carbon.
Small amounts of nitrogen and sulphur compounds are also present in coal.
Among fossil fuels, coal and petroleum are the most widely used.
They contain carbon and its compounds as the major constituents.
When the dead organic matter such as plants and animals are subjected to high pressure and temperature for a very long period of time under the earth’s surface they undergo decomposition and get converted to coal.
Thus coal and petroleum are continuously formed over millions of years by natural processes.
The process of conversion of dead organic matter into coal is referred to as carbonization because the major content of coal is carbon and the coal if formed from dead organic matter.
CHEMICAL PROPERTIES OF CARBON COMPOUNDS
COMBUSTION (OR BURNING)
Combustion is the process of burning of a carbon compound in air to give carbon dioxide; water, heat and light.
When methane (natural gas) burns in a sufficient air supply, then carbon dioxide and water vapour are forms producing a lot of heat:
Combustion of fuels are widely used across the various industries for the extraction of energy from them.
This energy is then used to operate different equipment’s, machineries, cooking etc.
Fuel in homes, transport and industry uses Methane (natural gas), as it produces a lot of heat on burning.
The color of the flame of combustion depends on the carbon compound being used.
Saturated hydrocarbons produce clean flame while unsaturated carbon compounds produce yellow flame with black smoke.
The burning of carbon compounds results in a sooty deposit on the surface or a sooty flame if there is an incomplete combustion of saturated hydrocarbons due to limited supply of air.
The saturated hydrocarbons (alkanes) generally burn in air with a blue, non-sooty flame.
The unsaturated hydrocarbons (alkenes and alkynes) burn in air with a yellow, sooty flame (producing black smoke):
Burning of unsaturated hydrocarbons in pure oxygen will result in complete burning to produce a blue flame (without any smoke at all).
Kerosene stove has inlets for the passage of air so that a mixture of oxygen and kerosene is burnt to give a clean blue flame.
The bottom of the vessel may be blackened indicating that the passage has been blocked and the fuel is almost wasted.
The oxygen– acetylene flame (called oxy-acetylene flame) is extremely hot and produces a very high temperature which helps in welding metals.
WHY MIXTURE OF ACETYLENE (ETHYNE) AND AIR IS NOT USED FOR WELDING?
Because burning of acetylene (ethyne) in air produces a sooty flame (due to complete combustion), which is not enough to melt metals for welding.
WHY IS THERE A DIFFERENCE IN BURNING COAL OR WOOD AND BURNING A CANDLE?
Candle burns with a flame and gives both heat and light but in case of coal/wood a red glow is observed without any flame.
This is because; a flame is observed only when a gaseous substance is burnt.
In a substitution reaction, one (or more) hydrogen atoms of a hydrocarbon replace some other atoms (like chlorine).
A less reactive element or molecule is replaced by a more reactive element or molecule.
Methane reacts with chlorine, in presence of sunlight.
Since Chlorine is more reactive it displaces the hydrogen atom from the saturated hydrocarbons to form chloromethane and hydrogen chloride:
The products formed are usually higher homologues of the same hydrocarbon
Addition reactions (like the addition of hydrogen, chlorine or bromine) are a characteristic property of unsaturated hydrocarbons or compounds that contain multiple bonds (double bond, triple bond) in them.
They react with hydrogen in the presence of catalysts to give saturated hydrocarbons .
A catalyst is a substance that enhances the rate of a chemical reaction without itself getting changed.
Addition of hydrogen transforms alkene to alkane.
Ethene reacts with hydrogen when heated in the presence of nickel catalyst to form ethane:
Hydrogenation is addition of hydrogen to unsaturated hydrocarbons.
The process of hydrogenation takes place in the presence of nickel or palladium metals as a catalyst.
HYDROGENATION OF OILS:
The process of hydrogenation has an important industrial application.
Preparation of vegetable ghee (or vanaspati ghee) from vegetable oils illustrates hydrogenation.
Heating of vegetable oil (like groundnut oil) with hydrogen in the presence of finely divided nickel as a catalyst results in the formation of saturated fat called vegetable ghee (or vanaspati ghee.
This reaction is hydrogenation of oils. Representation can be given as: