Question

what is a chemical reaction? what changes occure in a chemical reaction? give 5-6 examples of a chemical reaction.

Answer 1

Chemical reaction

A chemical reaction a is change in which one or more substance(s) or reactant(s) react(s) to form new substance(s) with entirely different properties.

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

Example

2 Na (s)  +  2 H₂O (l) → 2 NaOH (aq) + H₂ (s) ↑

Sodium      Water           Sodium        Hydrogen

                                      hydroxide

More examples -

3 Fe (s) + 4 H₂O (l )    →   Fe₃O₄ (s) + 4 H₂ (g)

2 Pb (NO₃) (s) → 2 PbO (s) + 4 NO₂ (g) + O₂ (g)

Na₂SO₄ (s) + BaCl₂ (s) → BaSO₄ (s) + 2 NaCl (s)

Answer 2

${\boxed{\tt{Chemical\:Reactions\:!!}}}$

The formation of new substances with Thier new properties is called chemical Reaction .

$\sf\small{Characteristics\:Of\:Chemical\:Reaction\:!}$

The Chemical reactions are often accompanied by some changes which can be easily observable changes (or features) which take place as a result of chemical reactions are known as characteristics of chemical reactions.

The important characteristics of chemical reactions are :-

• CHANGE IN STATE •

Some Chemical reactions are accompanied by change in state.

For Eg :- when Solid wax (in the form of a candle) is burned , then water vapour and carbon dioxide are formed, which are gaseous.

• CHANGE IN COLOUR •

Some Chemical reactions are accompanied by change in colour.

For Eg :- Lead nitrate and Potassium iodide are colourless but when these are mixed , a precipitate of yellow colour is formed . Similarly, in the rusting of nails, rust is brown in colour whereas nails were black .

• Formation of Precipitate •

Some Chemical reactions are accompanied by the formation of a precipitate .

For Eg :- When an aqueous solution of lead nitrate is mixed with an aqueous solution of potassium iodide, a yellow Precipitate of potassium iodide is formed.

• Evolution Of a Gas •

Some Chemical reactions are accompanied by the evolution of a gas.

For Eg :- Hydrogen has is evolved when zinc granules react with dilute sulphuric acid.

• Change in Temperature •

Some Chemical reactions are accompanied by change in temperature.

For Eg:- When water is added to quick lime taken in a beaker then slaked lime is formed. During this reaction, a lot of heat energy is produced and the reaction Mixture becomes hot.

• !!EXTRA INFORMATION !! •

There are some reactions in which temperature of reaction mixture decreases.

For Eg :- When barium hydroxide us added to ammonia chloride in a beaker, then the temperature of the reaction mixture decreases and the beaker becomes cold.

Over-all Your Conclusion is here !

• The chemical reactions takes place by the Change of State.
• The chemical reactions occur by Change of Colour.
• The chemical reactions occur by Formation of Precipitate.
• The chemical reactions occur with Evolution Of Gas.
• The chemical reactions occur with Evolution or absorption of Heat energy.

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