chemical changes and reaction

Question 1

what is a chemical change

Answer 1

Reaction in which chemical composition of a substance is changed and new substances with different chemical composition and properties are formed

Question 2

chemical reaction is the process of?

Answer 2

its the process of breaking chemical bonds of the reacting substance and form new bonds to form new substances

Question 3

what is a chemical bond

Answer 3

its the force holding atoms of a molecule together as in a compound

Question 4

name the conditions which are required for a chemical reaction

Answer 4

1)Mixing,2)electricity,3)solution,4)pressure,5)catalyst,6)heat,7)light

Question 5

what do you observe when lead nitrate decomposes

Answer 5

it leaves behind a yellow residue, brown gas nitrogen dioxide and colourless gas oxygen

Question 6

reactions taking place by action of light are called

Answer 6

photochemical reaction

Question 7

why is silver nitrate and hydrogen peroxide kept in brown bottles

Answer 7

They decompose in presence of light so they are kept in brown bottles

Question 8

what are electrochemical reaction

Answer 8

reactions occurring due to passage of electricity in the reactants are called electrochemical reactions

Question 9

when electricity is passed through molten sodium chloride what is observed

Answer 9

We obtain sodium and chloride seperatly

Question 10

what do you observe when you crush mercuric chloride and potassium iodide in a mortar?

Answer 10

a scarlet coloured substance called mercuric iodide is formed

Question 11

What are catalysts

Answer 11

Some substance accelerate or decelerate the rate of reaction without taking part in it such substances are called catalysts

Question 12

example of positive catalyst

Answer 12

manganese dioxide

Question 13

what are promoters

Answer 13

substances which improves the efficiency of the catalysts are called promoters

Question 14

what are the characteristics of a chemical reaction

Answer 14

1)evolution of gas,2)change in colour, 3)formation of precipitate,4)change in state

Question 15

name the types of chemical reactions

Answer 15

1) combination reaction, 2)decomposition reaction, 3) displacement reaction, 4) double displacement reaction

Question 16

What is dispalcement reaction

Answer 16

Reaction in which higher reactive substance takes place of a lesser active substance in its salt

Question 17

What is combination reaction

Answer 17

Reaction in which 2 reactants combine together to form one product

Question 18

What is decompostion reaction

Answer 18

Reaction in which one reactant breaks into 2 or more substance

Question 19

what is thermal decompostion

Answer 19

decomposition reaction bought about by heat is called thermal decompostion

Question 20

which metals on heating gives metal nitrate and oxygen

Answer 20

K, Na

Question 21

Name any 3 carbonates which decompose on heating with decreasing vigour to form metal oxide and co2

Answer 21

Ca,Mg,Al

Question 22

what do you observe when you heat up orange coloured ammonium dichromate

Answer 22

it decomposes with flashes of light forming nitrogen water vaporand a green solid chormium oxide