Notes of chemical reaction and equation | Class x [ i ]

1. Chemical Reaction:-

The transformation of chemical substance into another chemical substance.

Ex. ( rusting of iron, setting of milk into curd, digestion of food, respiration, etc.)

In chemical reaction new substance is formed which is completely different in properties from the original substance, so in a chemical reaction chemical change takes place.

Following are the signs of chemical reaction:

• Change of state of substance

• Change of color of substance

• Evolution of heat 

• Absorption of heat

• Evaluation of gas

• Evaluation of light

• Evaluation of sound, etc.

2. Reactant and product:-

Reactant: Substances which take part in a chemical reaction.

Product: New substance formed after a chemical reaction.

3. Chemical Equation:-

Representation of chemical reaction using symbols of substance

            Ex. ( A+B -> C+D)

In this equation, A and B are called reactants and C and D are called the products.

 

Arrow shows the direction of chemical reaction.

 

Condition, if any, is written generally above the arrow.

When hydrogen reacts with oxygen, it gives water.

The reaction can be represented by following chemical equation.

        Hydrogen + Oxygen -> Water

For convenience, symbols of substance is used to represent chemical equations.

                  H2 + O2 -> H2O

 Chemical Equation is a way to represent the chemical reaction in concise and informative way.

4. Types of chemical equation:-

• Balanced Chemical Equation.

A balanced chemical equation has number atoms of each element equal on both sides.

     Ex. ( Zn + H2SO4  -> ZnSO4 + H2

According to Law  of Conservation of Mass, mass can neither be created nor destroyed in a chemical reaction.

So, the total mass of elements present in reactants must be equal to the total mass of elements present in products.

  

• Unbalanced Chemical Equation.

An unbalanced chemical equation is the one in which the number of atoms of each element in reactants is not equal to the number of atoms of each element present in product.

           Ex. ( Fe + H2O -> Fe3O4 + H2)

5. Representing Physical State of substances in chemical equation:-

By writing the physical states of substances a chemical equation becomes more informative.

    Gaseous state is represented by symbol 'g'

    Liquid state is represented by symbol 'l'

    Solid state is written by symbol 's'

    Aqueous solution is written by symbol 'aq'

The condition is generally written above and/or below the arrow of chemical equation.

Ex. ( N2(g) + H2(g)  -> NH3(g).