Chemical Reactions and Equations (Class 10 Science) Part 1

Chemical Reactions

A chemical reaction is a change in which one or more substances or reactants reacts to to form new substances with different properties.

The reacting species (molecule, atom or ion) are known as reactants (the substances that undergo chemical change in the chemical reaction) and the new species formed as a result of the reaction are called products (the new substances formed during reaction).

 2Na(s) + 2H2O(l) → 2NaOH(aq) + H2(g)

In the above chemical reaction , sodium hydroxide and hydrogen are the products and sodium and water are the reactants.



Identification of chemical reaction

A chemical reaction can be identified by either of the following observations –

(i)                Change in state

(ii)             Change in colour

(iii)           Evolution of gas

(iv)           Change in temperature

(v)              Formation of precipitate


Chemical Equations


A chemical equation is the symbolic representation of a chemical reaction.

Methane  + Oxygen → Carbon dioxide + Water

This equation is called “ word equation”. The word equation can be changed in to a chemical equation by writting symbol and formulae of the substances in place of their name.

CH4(g) + 2O2(g) → CO2(g) + 2H2O(l)


Writing a Chemical Equation

A chemical equation shows a change of reactants to products through an arrow (→) placed between them.

On the left hand side (LHS) of the arrow reactants are written with a plus sign (+) between them. Similarly on the right hand side (RHS) , products are written  with a plus sign (+) between them.

            The arrow head points towards the products and shows the direction of the reaction.

Mg + O2 MgO

In the above equation, number of magnesium and oxygen atoms are not same on both sides of ab equation. Such an unbalanced equation is called skeletal chemical equation.

Part 2       Part 3

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