Selina Concise Class 7 Chemistry Solution Chapter No. 2- ‘Physical and Chemical Changes’ For ICSE Board Students.
1)
a)
i.)
Answer : A change in physical properties or condition like shape , size , state , of substance or temporary change without changing in chemical constituents are known as physical change.
ii) .
Answer :. A change to form one or more new substance from their original substance and they have different chemical properties from original one , this type of change known as a chemical change .
b)
Answer :i) Example of Physical Change :
- Water change into water vapour .
- Melting of wax .
- Making sugar Solution.
ii) Example of Chemical change:
- Rusting iron.
- Ripening of fruits .
- Formation of curd from milk
2)
Answer: i) Reversible Change :
A change of substance in which substance can be back to their original position are known as reversible changes .
Example : vaporization of water , dissolved salt in water , melting of wax etc.
ii) Irreversible change :
A change of substance in which substance can not be bring back to their original position are known as Irreversible changes.
Example : formation of curd from milk , Burning of paper , ripening of fruits etc.
3)
a)
Answer : Desirable Change :
A Change that are beneficial or useful for us known as desirable change .
Example : Ripening of fruits , formation of curd from milk .
b)
Answer : Undesirable Change :
A Change that are not beneficial or useful and harmful for us known as undesirable change .
Example : rusting of iron , tsunami , earthquake , Rotting of fruits .
c)
Answer : Periodic Change :
A change that occur regular or definite interval of time are known as periodic change .
Example : Day and night , changing phase of moon , change of seasons .
4)
Answer : Burning is a chemical change because when a substance burnt , new substance are formed which has different properties from original substance and it cannot be reversed to their original position .
5)
Answer : Burning of candle shows both physically and a chemical change because when candle is burnt wax of the candle melted and convert into liquid state , this melted wax can come back their original position (solid) when it get cooled , which is reversible, this is physical change But when candle is burnt there is carbon dioxide and water vapour are produced , So new substance are formed , and also energy is released in the form of light or heat , so this is chemical changes that’s why burning of candle are both physical and chemical change.
7)
Answer :
Sr.
No. |
Physical change | Chemical change |
1. | In physical change there is no change in a chemical properties of substance which are form by original one. | In a chemical change , chemical Properties are different from original one . |
2 | No new substance are formed . | One or more new substance are formed. |
3 | Physical change are temporary | Chemical change are permanent |
4 | In physical changes energy is not evolved . | In chemical change energy is evolved |
5 | It can be reversed by simple physical method. | It can not be reversed by simple physical method. |
8) a)
Answer : When water is boiled , Water change into steam or gas which is physical change.
b)
Answer : When a piece of paper is burnt , it produced carbon dioxide gas and ash which is chemical change .
c)
Answer : When some ice cube kept in glass tumbler , this ice cube change from solid state to liquid state , which is physical change.
d)
Answer : When solid ammonium chloride is heated , it change to vapour or gaseous state which is physical change.
e)
Answer : When iron nail is kept in a tap water for few days , radish brown counting ( rust) occur on the iron nail , new substance are formed on iron nail , so it is a chemical change.
f)
Answer : When spoon of sugar is heated in a pan , black substance ( carbon ) seen in the pan so it is a chemical change.
g)
Answer : When lighted match stick is brought near the test tube containing hydrogen gas , we observed blue flame and pop sound is heard , So it is a Chemical change.
h)
Answer : When quick lime is added to water we will observed that evolving large amount of heat energy , and hissing sound is heard , So it is a chemical change .
i)
Answer : When a little amount of curd is added to a bowl containing warm milk and kept for few hours , we will observe that milk changing into curd which is permanent change So it is a chemical change.
9)
a) Heat
Answer : i) Cooking of food need heat .
ii) burning of paper need heat
b) Light
Answer : i) formation of food by plants through photosynthesis process in presence of light.
ii) . Photo chemical reaction occur in presence of light .
c) Electricity
Answer : i) electrolysis reaction occur in presence of electricity that is water break into oxygen and hydrogen on passing electricity.
ii) The substance sodium chloride ( NaCl ) break down into Sodium (Na) and chlorine (Cl) by passing electric current through the substance .
Objective type questions
1) .
a) A new substance is always formed in a …………… change .
Answer : Chemical change
(When A change to form one or more new substance from their original substance and they have different chemical properties from original one , known as chemical change)
b) Melting of ice is a …………. Change .
Answer : Physical Change
(when ice is melt it convert to liquid state here only state of ice change so it is a physical change)
c) When a candle burns , wax melt , melting of wax is a ……….. change .
Answer : physical change
(when a candle burns wax melt and convert into liquid state , if this liquid get cool environment it will come back to original position so it is reversible , hence it is physical change)
d)Chemical change occur as a result of ………….. between two substance .
Answer : rearrangement
(Chemical change occur in a chemical reaction through rearrangement of atoms between two substance present in a reactant and form new product )
e) Burning of fuel is a ………….. change .
Answer : Chemical change
(when fuel is burnt , it produced heat energy , and carbon dioxide gas that is why it is a chemical change)
f) Revolution of the earth around the sun is the ……………. Change .
Answer : Periodic Change
(earth revolve around the sun regular or definite interval of , due to this change seasons , changing day and night , this change is known as periodic change .)
g) Growing of a seedling into a plant is a …………. Change .
Answer : Chemical change
(Growing of a seedling into a plant is a chemical change because it can not be reversible process and when plants grow many chemical reaction occur such a photosynthesis , respiration etc .)
b) 2) .
a)
Answer : Glowing of bulb – Physical Change
b)
Answer : Burning of sugar – chemical change
c)
Answer : heating of water – physical change
d)
Answer : growing of piglets into a pig – chemical change
e)
Answer : burning of wood – chemical change
f)
Answer : passing electric current through a heater rod – physical change
g)
Answer : Water cycle in nature – physical change
h)
Answer :Answer :respiration in living beings – chemical change
i)
Answer : Shaping a piece of glass – physical change
j)
Answer : lightning – chemical change
k)
Answer : dissolving sugar in water – physical change
l)
Answer : heating a mixture of iron filling and Sulphur – chemical change
m)
Answer :Mixing oil with water – physical change
n)
Answer : cutting wood into small pieces – physical change
o)
Answer : Photosynthesis – chemical change
p)
Answer : Digestion of food – chemical change
q)
Answer : melting of wax – physical change
r)
Answer :boiling of egg – chemical change
s)
Answer : slacking of lime – chemical change
3)
Answer :
Column A | Column B |
a) Evaporation of water | v) reversible change |
b) Milk turning sour | iii) chemical change |
c) Earthquake | i. )Non periodic change |
d) Changes of seasons | ii) Periodic Change |
e) Glowing of bulb | vi) Physical Change |
c) 4).
a)
Answer :False
b)
Answer : True
c)
Answer : False
d)
Answer : True
e)
Answer : False
Multiple choice questions
1)
Answer :3) Sugar
(Sublime substance heated solid is directly converted into gas , but when sugar is heated it left behind ash that is why sugar is not sublime substance )
2)
Answer : Condensation
(when you put some ice cube in glass droplets of water are formed on the outer wall of the glass , in the atmosphere water vapour are present when they get cool environment on the surface of glass it condense and water droplets are formed on the outer wall of the glass this process known as condensation )
3)
Answer : 2) fast process
( Burning is a fast process , in the atmosphere present oxygen help for burningsubstance , rapid oxidation occur when substance is burnt.)
4)
Answer : 2) Petrol
( The substance that rapidly evaporate known as volatile substance , example : petrol is a volatile substance)
5)
Answer : 1) burning of candle
(burning of candle is both physical and chemical changes , when candle is burnt wax is melt , melted wax is again come back to their original position which is reversible , so it is physical change , but when candle is , new substance likecarbon dioxide and water vapour are formed so it is chemical change)
6)
Answer : 3) iron
(When iron come in contact with moisture or water it get oxidised and rust form on iron surfaceor the compound rust is a hydrated oxide of iron )
7)
Answer : 3) black
(When sugar is heated it convert into carbon which is black in colour)
8)
Answer : 2) hydrogen
( a pop sound is heard when a lighted matchstick is brought near the mouth of the jar . This indicates that hydrogen gas released from the jar )
9)
Answer : 4) Quick lime
(When quick lime is added to water we will observed that evolving large amount of heat energy , and hissing sound is heard , So it is a chemical change.)