Type of Chemical Reactions
The topic “Type of chemical reaction” is very important to understand for all science students and the students who are going to appear in national talent hunt or scholarship entrance exams and other entrance exams. The topic “Type of chemical reaction” will help you to clear many of the doubts which were not cleared to you in earlier classes.”Type of chemical reaction” is the basic topic of chemistry so without studying it you can’t go in deep of the chemistry.
We have learned that during a chemical reaction atoms of one element do not change into atoms of another element, nor do atoms disappear from the mixture or appear from elsewhere. Actually, chemical reactions involve the breaking and making of bonds between atoms to produce new substances.
The second law of motion
The universal law of gravitational force
Type of Chemical Reactions
In this chemical reaction, two or more compounds form a single compound.In the following chemical reaction, Calcium oxide reacts vigorously with water to produce slaked lime (calcium hydroxide) releasing a large amount of heat.
In this reaction, calcium oxide and water combine to form a single product, calcium hydroxide. Such a chemical reaction in which a single product is formed from two or more reactants is known as a combination reaction.
There are several examples of combination reaction, as an example burning of coal, the formation of water from hydrogen and oxygen.
We also observe that in most of the combination reaction heat is evolved, such a combination reaction in which heat is also released known as exothermic reactions. So we can say every exothermic reaction is a combination reaction but it is not necessary that every combination reaction is exothermic, the exothermic reaction is a special case of combination reaction in which heat is released.
The formation of slaked lime with the release of heat from quick lime and water is an example of an exothermic reaction, burning of coal and formation of water are also the examples of exothermic reaction there are several examples of exothermic reactions, some of them are following.
(i) Burning of natural gas
(ii) Respiration reaction is an example of exothermic reaction. During digestion of food carbohydrate broken down into glucose, this glucose combines with oxygen in the cells of our body and forms carbon dioxide and water with the release of energy
This is the reaction in which one product is broken down into two or more products
In this reaction, you can observe that a single reactant breaks down to give simpler products. This is a decomposition reaction. Ferous sulphate crystals lose water when heated and the colour of the crystal changes from light green to white. On further heating white colour changes to dark brown due to the formation of black coloured solid substance ferric oxide , sulphur dioxide and sulphur trioxide . Ferric oxide is a solid, while and are gases.
Type of Decomposition reaction
(1) Thermal decomposition reaction-When a product is decomposed to simple products after heating it . Decomposition of calcium carbonate to calcium oxide and carbon dioxide on heating is an important thermal decomposition reaction used in various industries. Calcium oxide is called lime or quick lime. It has many uses – one is the manufacture of cement.
When potassium chlorate is heated it changes to potassium chloride and oxygen.
When ferric hydroxide heated it is decomposed into ferric oxide and water.
(2) Electrolysis-When an electric current is passed through an aqueous solution of a compound and it undergoes the process of decomposition then it is known as electrolysis.
The best example of electrolysis is the electrolysis of water and sodium chloride.
When an electric current is allowed to pass through water contained in an electrolytic device then water is decomposed into oxygen and hydrogen which collected at cathode and anode respectively.
When electrolysis occurs through an aqueous solution of sodium chloride, it is decomposed into sodium and chlorine, sodium is collected at cathode and chlorine is collected at the anode.
(3) Photo Decomposition- When sunlight is exposed to some substances then decomposition occurs known as photodecomposition.
Placing a small quantity of silver chloride on a glass plate, when sunlight is allowed to pass through it, the white crystals of silver chloride changes to grey color due to the decomposition of silver chloride into silver which is grey in color and chlorine.
Silver bromide also undergoes photodecomposition in the same way
The type of chemical reaction in which an atom of high reactive substance displaces an atom of less reactive substance from the molecule of another substance forming a new compound, such a reaction is known as displacement reaction.
Example-The iron nail dipped into the copper solution, changes the blue color of copper sulfate faded and changes to green color due to the displacement reaction.
In this reaction iron being more reactive than copper displaces copper atom ad substitutes it forming iron sulfate.
Other similar examples of displacement reactions are following.
Both of the above reaction shows that zinc and lead is more reactive than copper.
DOUBLE DISPLACEMENT REACTION
The reaction in which there are an exchange of ions between two reactants are called a double displacement reaction
An aqueous solution of sodium sulfate when allowed to mix up with the aqueous solution of barium chloride, an insoluble substance is formed which is precipitated at the bottom of the test tube, such a reaction is also known as a precipitation reaction
Oxidation is the loss of electrons during a reaction by a molecule, atom, or ion. Oxidation occurs when the oxidation state of a molecule, atom, or ion increased.
Oxidation is when iron combines with oxygen to form iron oxide or rust. The iron is said to have oxidized into rust.
The chemical reaction is:
The iron metal is oxidized to form the iron oxide known as rust.
The reduction is the gain of electrons during a reaction by molecule, atom or ion. Reduction occurs when the reduction state of a molecule, atom, or ion decreased.
The reaction between copper oxide and magnesium to yield copper and magnesium oxide:
A reaction in which one reactant undergoes oxidation whereas the other gets reduced during the course of reaction are termed as oxidation-reduction reactions or redox reactions.
Fe2O3 + 3CO ⇒ 3Fe + CO2
Here ferric oxide is reduced to iron and carbon monoxide is oxidized to carbon dioxide, ferric oxide is known as oxidizing agent and carbon mono oxide is a reducing agent.
You must have observed that iron particles are shiny when new, but for some time.get coated with a reddish row powder when left for some time. This process is commonly known as rusting of iron. Some other metals also get tarnished in this manner. Have you noticed the colour of the coating formed on copper and silver? When a metal is attacked by substances around it such as moisture, acids, etc., it is said to corrode and this process is called corrosion. The black coating on silver and the grey coating of copper are other examples of corrosion.
Corrosion causes damage to car bodies, bridges, iron railings, ships and to all objects made of metals, especially those of iron. Corrosion of iron is a serious problem. Every year an enormous amount of money is spent to replace damaged iron.
Have you ever tasted or smelt the fat/oil containing food materials left for a long time?
When fats and oils are oxidized, they become rancid and their smell and taste change. Usually, substances that prevent oxidation (antioxidants) are added to foods containing fats ad oils. Keeping food in airtight containers helps to slow down oxidation. Do you know that chips manufacturers usually flush bags of chips with gas such as nitrogen to prevent the chips from getting oxidized?