Name: Types of Chemical Reactions
Uploaded: 2019-07-19
Duration: 7 min 20 s
Description: Each chemical reaction has its own way of proceeding and a distinct way the reactants interact with each other according to which they are classified. Watch...

Question

State the main characteristics of chemical reactions. Give at least one example in each case.

Accepted Answer

The main characteristics of chemical reactions are as follows:

1. Evolution of gas: In many chemical reactions, one of the products is a gas. For example, when zinc reacts with dilute sulphuric acid, hydrogen gas is evolved with effervescence. The chemical equation is as follows:

$\underset{Zinc}{Zn} + \underset{dil . sulphuric acid}{H_{2} {SO}_{4}} \to \underset{zinc sulphate}{{ZnSO}_{4}} + \underset{hydrogen}{H_{2} ↑}$

2. Change of colour: Certain chemical reactions are characterised by a change in the colour of the reactants. For example, when a few pieces of iron are dropped into a blue coloured copper sulphate solution, the blue colour of the solution fades and eventually turns into light green due to the formation of ferrous sulphate. The chemical equation is as follows:

$\underset{iron}{Fe} + \underset{blue solution}{{CuSO}_{4} (aq)} \to \underset{green solution}{{FeSO}_{4}} + \underset{copper (brown deposit)}{Cu}$

3. Formation of precipitate: Certain chemical reactions are characterised by the formation of insoluble solid substances called precipitates. For example, when ferrous sulphate solution is added to sodium hydroxide solution, a dirty green precipitate of ferrous hydroxide is formed. The chemical equation is as follows:

$\underset{Ferrous sulphate}{{FeSO}_{4} (aq)} + \underset{Sodium hydroxide}{2 NaOH (aq)} \to \underset{Ferrous hydroxide (dirty green ppt)}{Fe {(OH)}_{2} ↓} + \underset{Sodium sulphate}{{Na}_{2} {SO}_{4} (aq)}$

4. Change of state: In many chemical reactions, a change of state is observed. A reaction might start with gaseous or liquid reactants and end up with solid products, or vice versa. For example, ammonia gas reacts with hydrogen chloride gas to produce solid ammonium chloride. The chemical equation is as follows:

${NH}_{3} (g) + HCl (g) ⇄ {NH}_{4} Cl (s)$

State the main characteristics of chemical reactions. Give at least one example in each case.

Important Questions on Chemical Changes and Reactions

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