Chemical reaction and equation

                   CHAPTER NUMBER I

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CHEMICAL REACTION AND EQUATION 

* Chemical reaction :-

            

 A chemical reaction is a process in which one or more substances are converted into one or more different substances. During a chemical reaction, the bonds between atoms in the reactants are broken and new bonds are formed to create the products. 

Chemical reactions can be represented by chemical equations, which show the reactants on the left-hand side of the equation and the products on the right-hand side. For example, the chemical equation for the reaction between hydrogen gas (H2) and oxygen gas (O2) to form water (H2O) is: 

2H2 + O2 → 2H2O 

This equation shows that two molecules of hydrogen gas and one molecule of oxygen gas react to form two molecules of water. 

* Chemical reactions can be classified into different types based on the changes that occur during the reaction,

 *such as changes in energy,

 *changes in composition, 

*changes in color, 

*and changes in state.

 ->Some common types of chemical reactions include combustion reactions, decomposition reactions, single and double displacement reactions, and acid-base reactions. 

-->Types of chemical reactions:

1. Combination reactions: These reactions occur when two or more reactants combine to form a single product. The general form of a combination reaction is:

A + B → AB

Example 1) CaO(s) + H2O (l) -----> Ca(OH)2

     2) 2H2(g) + O2(g) ------->2 H2O(l)

An example of a combination reaction is the reaction between iron and sulfur to form iron sulfide:

Fe + S → FeS

2. Decomposition reactions

These reactions occur when: en:  a single reactant breaks down into two or more products. The general form of a decomposition reaction is:

AB → A + B

An example of a decomposition reaction is the breaking down of water into hydrogen gas and oxygen gas:

2H2O → 2H2 + O2

Example 2) FeSO4(s) ------->Fe2O3(s) + SO2(g) + SO3(g)

Example 3) CaCO3(s) -------> CaO(s) + CO2(g)

Example 4) Pb(NO3)2(s)------>PbO(s) + NO2(g) + O2(g)

3. Displacement reactions:

 In these reactions, one element takes the place of another element in a compound. There are two types of displacement reactions:

- Single displacement reactions: In these reactions, a single element replaces another element in a compound. The general form of a single displacement reaction is:

A + BC → AC + B

An example of a single displacement reaction is the reaction between zinc and hydrochloric acid to form zinc chloride and hydrogen gas:

Example 1) Zn + 2HCl → ZnCl2 + H2

Example 2) Fe(s) + CuSO4(aq)------> FeSO4(aq) + Cu(s)  

4) Double displacement reactions: In these reactions, the cations and anions of two different compounds switch places. The general form of a double displacement reaction is:

AB + CD → AD + CB

An example of a double displacement reaction is the reaction between sodium chloride and silver nitrate to form silver chloride and sodium nitrate:

NaCl + AgNO3 → AgCl + NaNO3

4. Combustion reactions: These reactions occur when a substance reacts with oxygen gas, usually producing heat and light. The general form of a combustion reaction is:

A + O2 → CO2 + H2O

An example of a combustion reaction is the burning of methane gas in the presence of oxygen:

CH4 + 2O2 → CO2 + 2H2O

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