These are the CBSE class 10 Chemistry notes on chapter Chemical Reactions and Equations Topics covered in this page are
Some of the important types of chemical reactions are:
Those reactions, in which two or more substances combine to form a single substance, are called combination reactions.
Examples:Hydrogen burns in oxygen to form water:
In this reaction, two elements, hydrogen and oxygen are combining to form single compound water, so this is an example of a combination.
In this reaction, two compounds, ammonia and hydrogen chloride, combine together to produce a new compound ammonium chloride. So, this is a combination reaction.
In this reaction, carbon dioxide compound reacts with oxygen element to form a new compound, carbon dioxide. So, this is a combination reaction.
Those reactions in which a compound splits up into two or more simpler substances are known as decomposition reactions.The decomposition reactions are carried out by applying heat, light or electricity.
In this reaction, one substance, calcium carbonate is breaking up into two simpler substances, calcium oxide and carbon dioxide, so this is a decomposition reaction.
When a decomposition reaction is carried out by heating, it is called ‘thermal decomposition’.Example: When lead nitrate is heated strongly, it breaks down to form simpler substances like lead monoxide, nitrogen oxide and oxygen.
Some decomposition reactions are carried out by using electricity.Example: When electric current is passed through acidified water, it decomposes to give hydrogen gas and oxygen gas.
This decomposition reaction takes place by the action of electricity. It is called electrolysis of water.
Some decomposition reactions are carried out by light energy.Example: When silver chloride is exposed to light, it decomposes to form silver metal and chlorine gas.
In this reaction, zinc displaces copper from copper sulphate compound so that copper is free. This displacement reaction takes place because zinc is more reactive than copper.
In this reaction, iron displaces copper from copper sulphate solution. The deep blue colour of copper sulphate solution fades due to the formation of green solution of iron sulphate. A red-brown coating (or layer) of copper metal is formed on the surface of iron metal (or iron nail).
Example:When barium chloride solution is added to sodium sulphate solution, then a white precipitate of barium sulphate is formed along with sodium chloride solution.
In this reaction, two compounds barium chloride and sodium sulphate react to form two new compounds, barium sulphate and sodium chloride. An exchange of ions takes place in this reaction.
In this reaction, barium sulphate is formed as a white, insoluble solid called precipitate which separates out suddenly from the solution.
Note: any reaction in which an insoluble solid called precipitate is formed that separates from the solution is called a precipitation reaction.
When copper oxide is heated with hydrogen, then copper metal and water are formed.
In the above reaction, copper oxide (CuO) is changing into copper (Cu), so copper oxide is being reduced to copper.
Hydrogen is changing into water (H2O), so hydrogen is being oxidized to water.
Copper oxide is giving oxygen required for the oxidation of hydrogen, therefore, copper oxide is oxidizing agent and hydrogen is reducing agent.
Effect of oxidation reactions in everyday life:
Oxidation has damaging effect on metals as well as on food. There are two common effects of oxidation reactions which we observe in daily. These are:
Corrosion of metals:
Corrosion is the process in which metals are eaten up gradually by the action of air, moisture or a chemical (such as an acid) on their surface.
Rancidity can be prevented by adding anti-oxidants to foods containing fats and oils:
Anti-oxidant is a substance (or chemical) which prevents oxidation. Anti-oxidants are actually reducing agent.
The two common anti-oxidants used in foods to prevent the development of rancidity are BHA (Butylated Hydroxy – Anisole) and BHT (Butylated Hydroxy-Toluene).
Rancidity can be prevented by packaging fats and oils containing foods in nitrogen gas:
When the packed is surrounded by unreactive gas nitrogen, there is no oxygen to cause its oxidation and make it rancid.
The manufacturers of potato chips fill the plastic bags containing chips with nitrogen gas.