Viraf J. Dalal solutions for New Simplified Middle School Chemistry [English] Class 8 chapter 2 - Physical & Chemical Changes [Latest edition]

Change is the law of nature which occurs in everyday life.
State when a substance [i.e. matter] undergoes a kind of change. 

Give a reason why

Freezing of water is a reversible change while burning of a candle – an irreversible change.

Give a reason why

Change of seasons is a periodic change while the change of weather is a non-periodic change.

State which of the following pertain to – chemical changes.

(a) Substance retains its identity
(b) The change is permanent
(c) No new substance is formed
(d) Is easily reversible
(e) Produces one or more new substances by a change in its composition
(f) The change is temporary
(g) The composition and properties of the original substance are not altered.

Give four reasons why the burning of a magnesium ribbon in the air is considered a chemical change.

Compare the energy changes involved during a physical and a chemical change.

Is a change of state of matter – a physical or a chemical change. Give reasons.

State which of the following terms connected with change of state of matter i.e.

(a) Melting
(b) Vaporisation
(c) Condensation
(d) Freezing

pertain to –

1. Conversion of a liquid into a vapour or gas.
2. Conversion of a liquid into a solid.
3. Conversion of a solid into a liquid on heating.

Potassium chloride is added to water and stirred. A salt solution is obtained, which is then boiled, leaving behind a residue.

1. Is the above change physical or chemical?
2. Name the residue which remains behind after the salt solution is boiled.
3. Is the change reversible or not reversible?
4. Are the composition and properties of the original substance altered?
5. Give a reason why the above experimentation would not be possible if calcium carbonate was taken in place of potassium chloride.

Give a reason why – Heating a platinum wire is a reversible change but, heating a magnesium wire is an irreversible change.

Give a reason why – Addition of zinc nitrate to water is a physical change but, the addition of zinc to dilute nitric acid is a chemical change.

Give a reason why – Rusting of iron is a chemical change but, the magnetization of iron is a physical change.

Select the chemical changes from the following list of changes

Vaporisation of water into water vapour.

Select the chemical changes from the following list of changes

Boiling of milk. 

Select the chemical changes from the following list of changes

Respiration in mammals.

Select the chemical changes from the following list of changes

Rotting of eggs.

Select the chemical changes from the following list of changes

Drying of a fruit

Select the chemical changes from the following list of changes

The carbon cycle.

Select the chemical changes from the following list of changes

The occurrence of lightning.

Select the chemical changes from the following list of changes

Breaking of glass

Select the chemical changes from the following list of changes

Butter turning rancid

Select the chemical changes from the following list of changes

Glowing of an electric bulb.

Select the chemical changes from the following list of changes

The crystallisation of salt from its solution.

Select the chemical changes from the following list of changes

Change of seasons

Select the chemical changes from the following list of changes

Preparation of carbon dioxide from calcium carbonate & dilute hydrochloric acid.

Select the correct answer from the choice given below to complete the sentence

A change in which a substance retains its identity is a

______ change.

Select the correct answer from the choice given below to complete the sentence

The matter is added or removed during a ____________  change.

Select the correct answer from the choice given below to complete the sentence

The energy required for completion of a physical change is ______________ when the change is reversed.

Select the correct answer from the choice given below to complete the sentence

The dissolution of lead nitrate in water is deemed as a _________ change.

A change in which matter undergoes a change but the total mass of the substance is unaltered is a ______ change.

State which of the following 1 to 5 pertain to – A: Physical Change B: Chemical change :

1. Sublimation.
2. Fermentation.
3. Liquefaction or condensation.
4. Magnetization.
5. Respiration.

Give the reason why the following is considered as chemical changes.

Copper carbonate on heat gives copper oxide and carbon dioxide.

Give the reason why the following is considered as chemical changes.

A bright light is seen evolved when a strip of magnesium is heated.

Give the reason why the following is considered as chemical changes.

Sulphur when burnt in air evolves a gaseous acidic product.

Give the reason why the following is considered as chemical changes.

An iron nail kept open in the atmosphere rusts.

Give the reason why the following is considered as chemical changes.

A piece of magnesium strip is dropped into a beaker containing dilute hydrochloric acid.

Match the examples of changes in List I with the correct type of change in List II.

Name the following.

The salt obtained when a chemical change takes place on the addition of iron to dilute sulphuric acid.

Name the following.

The product obtained during a physical change when water converts from a liquid into a solid.

Name the following.

The product of the chemical change in keeping a polished iron nail exposed to the atmosphere.

Name the following.

A form of energy required for a chemical change.

Name the following.

The gaseous product of the chemical change which takes place during respiration in living organisms.