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

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Solution

The main characteristics of a chemical reaction are:
(a) Evolution of gas:
In many chemical reactions, one of the product is a gas

$Z n (s)$ + $H_{2} S O_{4} (a q)$ $\to$ $Z n S O_{4} (s)$ + $H_{2} (g)$
(b) Change of colour
A certain chemical reaction is characterized by a change in the colour of the reactants.

$F e (s)$ + $C u S O_{4} (a q)$ $\to$ $F e S O_{4} (a q)$ + $C u (s)$

(c) Formation of precipitates
Certain chemical reactions are characterized by the formation of an insoluble substance called precipitates.

$A g N O_{3} (a q)$ + $N a C l (a q)$ $\to$ $A g C l (p p t)$ + $N a N O_{3} (a q)$

(d) Change of state
In many chemical reactions, a change of state is observed. The reaction might start with gaseous or liquid reactants and end with a solid product and vice-versa.

$N H_{3} (g)$ + $H C l (g)$ $\to$ $N H_{4} C l (s)$

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Similar questions

(a) Give one example of a chemical reaction.

(b) State two characteristics of the chemical reaction which takes place when dilute sulphuric acid is poured over zinc granules.

(c) Give two characteristics of the chemical reaction which occurs on adding potassium iodide solution to lead nitrate solution.

Give one example each of which illustrates the following characteristics of a chemical reaction:

(a) Evolution of a gas
(b) Change of colour

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