When a chemical change occurs a chemical reaction is said to have taken place. A chemical reaction can be represented with the help of symbols and formula which is known as chemical equation. The details about chemical equation and its significances are discussed in language of chemistry.
A chemical reaction can be induced by various techniques. Some chemical reaction
occurs as soon as the reactants comes into contact while other may require a drastic condition to bring about a chemical reaction. The different methods of bringing a chemical reaction are briefly described below.
1. By simple contact:
A contact of the reactants is the essential condition for any chemical reactions. Reactants whatsoever reactive may be, they will not react unless they come into contact. For example, phosphorus and iodine can be kept side by side without any reaction but as soon as they some into contact thry react together to give phosphorus tri-iodide.
2. By contact through solution:
Certain reaction does not occur by simple contact in solid but they have to be brought into contact through solution. For example, tartarie acid and sodium bicarbonate powder can be kept together without any reaction .but when they are brought together through the solution they react together vigorously with effervescence evolving carbon dioxide gas.similarly
silver nitrate and sodium chloride do not react in solid state but they immediately react together
giving precipitate of silver chloride when they are brought together in solution.
3. By application of heat:
Generally heat accelerates a chemical reaction. sometimes application of heat is essential to bring about some chemical reaction.for example copper turning and conc. sulphuric acid do not react in cold but when heated they react together producing sulphur dioxide gas.some of the example are decomposition of potassium chlorate,mercuric oxide by heat. such reaction are called thermal decomposition.
4. By application of pressure:
Certian reaction occurs when pressure is applied.foe example potassium chlorade and sulphur react together producing a loud noise when rubbed in mortar by pestle with pressure.usually gaseous reaction are carried out under pressure.for example in the synthesis of ammonia by haber process as high as 400 atmosphere is used.
5. By application of electricity:
Electricity can bring about many important chemical reaction. for example, when eletricity is passed through acidulated water, water splits into hydrogen and oxygen.
sodium metal is prepared be eletrolysis of molten sodium chloride and many metals are purified be eletriolysis process.
6. By irradiation of light:
Certian reaction occurs in presence of light only. Such reactions are called phototchemical reactions. Photosynthesis is a very important reaction occuring in nature which is brought by light . In photosynthesis reaction, carbon dioxide and water combine in green plant in presence of light. The photography is also based on the reaction brought about by light . Methane combines with chlorine in diffuse sunlight to givessubstitution product.
7. By use of catalyst:
Many industrially important reactions are carried out in presence of catalyst. Catalyst increases the speed of a reaction. For example, in the manufacture of ammonia by Haber process , iron is used as catalyst. Similarly. in the manufacture of vegetable ghee , nickel is used as catalyst. Other important catalyst are platinum, rhodium, etc. We will hardly find any industrial process where some kind or other kind of catalyst is not used. During combustion of petrol in automobiles some amount of poisonous gas like carbon monoxide comes out in automobiles exhaust which pollutes the atmosphere. Owing to this, catalyst is incorporated in the exhaust system in automobiles in advanced countries to convert carbon monoxide to carbon dioxide. Hydrogen peroxide decomposes slowly on its own giving oxygen and water. In presence of manganese dioxide this reaction occurs with greater speed.
A chemical reaction can be induced by various techniques. Some chemical reaction
occurs as soon as the reactants comes into contact while other may require a drastic condition to bring about a chemical reaction. The different methods of bringing a chemical reaction are briefly described below.
1. By simple contact:
A contact of the reactants is the essential condition for any chemical reactions. Reactants whatsoever reactive may be, they will not react unless they come into contact. For example, phosphorus and iodine can be kept side by side without any reaction but as soon as they some into contact thry react together to give phosphorus tri-iodide.
2. By contact through solution:
Certain reaction does not occur by simple contact in solid but they have to be brought into contact through solution. For example, tartarie acid and sodium bicarbonate powder can be kept together without any reaction .but when they are brought together through the solution they react together vigorously with effervescence evolving carbon dioxide gas.similarly
silver nitrate and sodium chloride do not react in solid state but they immediately react together
giving precipitate of silver chloride when they are brought together in solution.
3. By application of heat:
Generally heat accelerates a chemical reaction. sometimes application of heat is essential to bring about some chemical reaction.for example copper turning and conc. sulphuric acid do not react in cold but when heated they react together producing sulphur dioxide gas.some of the example are decomposition of potassium chlorate,mercuric oxide by heat. such reaction are called thermal decomposition.
4. By application of pressure:
Certian reaction occurs when pressure is applied.foe example potassium chlorade and sulphur react together producing a loud noise when rubbed in mortar by pestle with pressure.usually gaseous reaction are carried out under pressure.for example in the synthesis of ammonia by haber process as high as 400 atmosphere is used.
5. By application of electricity:
Electricity can bring about many important chemical reaction. for example, when eletricity is passed through acidulated water, water splits into hydrogen and oxygen.
sodium metal is prepared be eletrolysis of molten sodium chloride and many metals are purified be eletriolysis process.
6. By irradiation of light:
Certian reaction occurs in presence of light only. Such reactions are called phototchemical reactions. Photosynthesis is a very important reaction occuring in nature which is brought by light . In photosynthesis reaction, carbon dioxide and water combine in green plant in presence of light. The photography is also based on the reaction brought about by light . Methane combines with chlorine in diffuse sunlight to givessubstitution product.
7. By use of catalyst:
Many industrially important reactions are carried out in presence of catalyst. Catalyst increases the speed of a reaction. For example, in the manufacture of ammonia by Haber process , iron is used as catalyst. Similarly. in the manufacture of vegetable ghee , nickel is used as catalyst. Other important catalyst are platinum, rhodium, etc. We will hardly find any industrial process where some kind or other kind of catalyst is not used. During combustion of petrol in automobiles some amount of poisonous gas like carbon monoxide comes out in automobiles exhaust which pollutes the atmosphere. Owing to this, catalyst is incorporated in the exhaust system in automobiles in advanced countries to convert carbon monoxide to carbon dioxide. Hydrogen peroxide decomposes slowly on its own giving oxygen and water. In presence of manganese dioxide this reaction occurs with greater speed.
