10th Class Science Chemical Reactions and Equations Chemical Reactions

       Introduction

In this chapter we will study about chemical reactions and equations, balancing of equations, types of chemical reactions, effects of oxidation in daily life and many more.

         Chemical Reactions

Let us consider the two process:

• Dissolution of sugar in water and
• Cooking of food.

In the first process the properties of both sugar and water are present in the solution and no new chemical compound is formed, so it is a physical change. On the other hand in the second process that is cooking of food, the ingredients loose their nature and form a new substance with different properties is formed so this is called a chemical change.

The chemical changes are the outcome of chemical reactions. So the chemical reaction can be defined as the change of one or more substance into other substances having different chemical composition and properties.

For example. Hydrogen (gas) + Chlorine (g) \[\to \] Hydrogen chloride (g)

\[{{H}_{2}}+C{{l}_{2}}\to 2HCl\]

• The substances which takes part in a chemical reaction are called reactants.
• The substances which are produced during a chemical reaction are called products.

Carbon _(s) + Oxygen (g) \[\to \] Carbon dioxide

\[{{C}_{2}}+2{{O}_{2}}\to 2C{{O}_{2}}\]

         Characteristics of Chemical Reactions

Some of the important characteristics of chemical reactions are:

• Change of state

Hydrogen + Oxygen \[\to \] water.

\[2{{H}_{2(g)}}+{{O}_{2(g)}}\to 2{{H}_{2}}{{O}_{(I)}}\]

• Evolution of gas

When sodium reacts with water, bubbles of hydrogen gas is seen.

\[2Na+2{{H}_{2}}O\to 2NaOH+{{H}_{2}}\]

• Change in colour

When iron rail is dipped in blue coloured copper sulphate solution, the blue color changes to green.

\[Fe+CuS{{O}_{4}}\to FeS{{O}_{4}}+Cu\]

• Change in temperature

When water is added to quick lime the mixture becomes hot due to evolution of heat.

\[CaO+{{H}_{2}}O\to Ca{{(OH)}_{2}}+Heat\]