Tag: classification of changes

Questions Related to classification of changes

Small gaps are left between the metal rails on railway tracks in order to allow for :

chemistry changes around us can all changes be reversed? substances and objects classification of changes

  1. expansion of the metal rails on cold days

  2. contraction of the metal rails on hot days

  3. contraction of the metal rails on cold days

  4. expansion of the metal rails on hot days

Show answer
Correct Option: D
Explanation:
All metals expand when heated. If two railway tracks are laid together without any gap between them they will push against each other when they expand in the day time because of the heat of the sun, and when they cool down in the night they will contract and return to their original state pulling against each other. 
This constant pushing and pulling against one another when they heat and expand in the day time and cool down and contract in the night will result in the weakening of the joints between the two tracks and after a few days the two tracks may also break free from one another.
Such a situation will result in the derailment of the trains causing major accidents and loss of lives.

To prevent this, the railway engineers always leave a small gap between two rails to compensate for the expansion of the rails during the hot day time and contraction during cold nights.

Hence, the correct option is $\text{D}$

The density of a certain solid object is greater than the density of the liquid. If  it is placed in water, the object will :

chemistry changes around us can all changes be reversed? substances and objects classification of changes

  1. sink

  2. expand

  3. float

  4. contract

Show answer
Correct Option: A
Explanation:

When solid is placed in water, the density of solid decides if it will float or sink in water. 


If the density of solid is higher than liquid water it sinks because according to Archimedes principle, the buoyancy force is not enough to hold it in place.

i.e. if solid density > liquid - sinks

     if solid density < liquid - floats


Hence the correct option is A.

Which of the following is true about dissolving:

chemistry changes around us can all changes be reversed? substances and objects classification of changes

  1. Dissolving is an example of a reversible change.

  2. Dissolving is an example of a irreversible change.

  3. It depends on the conditions of dissolution.

  4. None of the above.

Show answer
Correct Option: A
Explanation:

Dissolving is an example of a reversible change. When salt is mixed with water it disappears because it dissolves in the water to make salty water. But we can get the salt can back again by boiling off the water. That leaves the salt behind.

Railway tracks have gaps between them to deal with expansion in :

chemistry changes around us can all changes be reversed? substances and objects classification of changes

  1. hot days

  2. cold days

  3. winters

  4. snow fall

Show answer
Correct Option: A
Explanation:

The railway tracks are made up of metals and hence they have a property of expansion when heated and contraction when cooled.

$\therefore $  Railway tracks have gap between them to deal with expansion during hot days.

Heating will produce what sort of change?

chemistry changes around us can all changes be reversed? substances and objects classification of changes

  1. An irreversible change

  2. A reversible change

  3. Either a reversible or irreversible change

  4. Neither a reversible or irreversible change

Show answer
Correct Option: C
Explanation:

Either reversible or irreversible change.

Reversible $-$ if there is a change of state for eg. melting, boiling 
           ${ H } _{ 2 }{ O } _{ \left( l \right)  }\rightleftharpoons { H } _{ 2 }{ O } _{ \left( g \right)  }$
Irreversible $-$ if the structural arrangement of the atom is changed.
eg : Burning of wood, kerosene etc.

What is a reversible change?

chemistry changes around us can all changes be reversed? substances and objects classification of changes

  1. A material changes permanently into a new material

  2. A material changes its feel or appearance, but it is still the same material

  3. A material changes into a new material, but it can be changed back

  4. A material stops existing

Show answer
Correct Option: C
Explanation:

A reversible change is a physical change that can be undone. 
A final substance can be converted back to the original substance without creating any new material.
An irreversible change is a permanent change that cannot be undone.
Option A is irreversible change.
Option C is reversible change.
The correct answer is option C.

The change of state of water from one form to another is :

chemistry changes around us can all changes be reversed? substances and objects classification of changes

  1. chemical change

  2. irreversible change

  3. reversible change

  4. state variation

Show answer
Correct Option: C
Explanation:
The change of state in water is a physical change hence it is reversible. When water is heated it convert in vapours and when cooled till $0^o C$ it freezes to form ice. Water vapors on condensation converts into water.

Hence the option C is correct.

Consider the expansion and contraction among solids, liquids and gases, the one which has a greater tendency to expand is :

chemistry changes around us can all changes be reversed? substances and objects classification of changes

  1. solid

  2. liquid

  3. gas

  4. none of these

Show answer
Correct Option: C
Explanation:

Gases have a greater tendency to expand because it has no or negligible intermolecular force of attraction between the particles. 


Hence, they can move easily, resulting in expansion whereas solid has a compact structure, they have the least tendency to expand.

Hence the correct option is C.

Brown colour of the apple after cutting is:

chemistry changes around us can all changes be reversed? substances and objects classification of changes

  1. physical change

  2. biological change

  3. chemical change

  4. no change

Show answer
Correct Option: C
Explanation:

The brown colour of the apple after cutting is due to the chemical change of the enzymes.
When an apple is cut, oxygen is introduced into the injured plant tissue. When oxygen is present in the cells, polyphenol oxidase enzymes(PPO) in the chloroplasts rapidly oxidize phenolic compounds naturally present in the apple tissues to o-quinones, colourless precursors to brown coloured secondary products. o- quinones then produce the brown colour by reacting to form compounds with amino acids or proteins they self-assemble to make polymers.

When a nail is added to acidic copper sulphate solution, the colour changes from _______.

chemistry phenomena around us changes and its classification types of changes classification of changes

  1. blue to green

  2. green to blue

  3. blue to pink

  4. pink to green

Show answer
Correct Option: A
Explanation:

When a nail is added to acidic copper sulphate solution, the colour changes from blue to green.
Copper sulphate reacts with iron to form iron sulphate.