• Can all changes be reversed? - class-VII
Back
0

Can all changes be reversed? - class-VII

Description: can all changes be reversed?
Number of Questions: 19
Created by:
Tags: changes around us changes around us substances in daily use chemistry
Start the Quiz
Attempted 0/19 Correct 0 Score 0
‹
›

All chemical reactions are :

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

  1. reversible

  2. irreversible

  3. exothermic

  4. endothermic

Show answer
Correct Option: B
Explanation:

A change in which one or more than one new substances are formed is known as a chemical change. 


A chemical change is also called a chemical reaction. Chemical reactions are not reversible.

Hence the option B is correct.

Sheet erosion is due to _________.

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

  1. fast running rivers

  2. heavy rains

  3. occasional rains

  4. wind

Show answer
Correct Option: B
Explanation:

Sheet erosion is the detachment of soil particles by raindrop impact and their removal downslope by water flowing overland as a sheet instead of in a definite channel.


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

Which of the following changes are irreversible?

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

  1. Milk to paneer

  2. Cow dung to biogas

  3. Grain to its flour

  4. All of the above

Show answer
Correct Option: D
Explanation:

All of the following changes are irreversible because we can not convert the product into reactant again.
1) Milk to paneer.
2) Cow dung to biogas.
3) Grain to its flour.

 Iron adopts changes slowly and gradually by process of :

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

  1. rusting

  2. moldings

  3. fermentation

  4. explosions

Show answer
Correct Option: A
Explanation:
Iron adopt changes slowly and gradually when it comes in contact with air (moisture, oxygen etc)
When Iron reacts with $'n'$ molecules of water in the pressure of oxygen, it forms rust. Hence the process is known as a rusting.
$4Fe+3{ O } _{ 2 }+2n{ H } _{ 2 }O\longrightarrow 2{ Fe } _{ 2 }{ O } _{ 3 }.n{ H } _{ 2 }O$

 Burnt sparklers and burnt books pages are examples of 

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

  1. reversible change

  2. irreversible change

  3. no change

  4. none of the above

Show answer
Correct Option: B
Explanation:

Burnt sparklers and burnt books pages are examples of irreversible changes, as they are permanent changes which cannot be undone. Once these materials are burnt in to ashes, the original materials cannot be recovered back.

Which of the following is not a reversible change?

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

  1. Heating of water to steam

  2. Cooking of egg to scrambled eggs

  3. Heating of wax to molten wax

  4. Cooling a cake

Show answer
Correct Option: B

Which of the following change cannot be reversed ?

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

  1. Hardening of cement

  2. Freezing of ice cream

  3. Opening a door

  4. Melting of choclate

Show answer
Correct Option: A
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.


A. Hardening of cement is an irreversible change as we cannot reverse back to the original cement powder form once the cement hardens.
B. Freezing of ice-cream is reversible change as it can be reversed back by heating and it will convert to original form.
C. Opening of a door is reversible change as it can be reversed simply by closing the door 
D. Melting of chocolate is reversible change as it can be reversed by cooling the chocolate to its original form.
Option A is the correct answer.

Burnt sparklers and burnt books pages are examples of:

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

  1. reversible process

  2. irreversible process

  3. rusting

  4. none of these

Show answer
Correct Option: B
Explanation:

Irreversible changes $-$ because when they are burnt formation of gas and ashes takes place i.e. chemical reaction is taking place and new substance are formed which can't be reversed back.


      Book pages  $\quad \xrightarrow { \text{burning} } \quad { CO } _{ 2 }+$ other substances.

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

Which of the following changes are irreversible?

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

  1. Raw egg to boiled egg

  2. Woollen yarn to knitted sweater

  3. Bud to flower

  4. All of the above

Show answer
Correct Option: D
Explanation:

The following changes are irreversible.We cant covert product into reactant in these processes

1) Raw egg to boiled egg.
2) Woollen yarn to the knitted sweater.
3) Bud to flower.

Which of the following represents a reversible change?

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

  1. A metal rod on heating expands (its length increases).

  2. A metal rod on cooling contracts (its length decreases).

  3. Both of the above

  4. None of the above

Show answer
Correct Option: C
Explanation:

The following represents a reversible change. A metal rod on heating expands (its length increases). A metal rod on cooling contracts (its length decreases).

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.

- Hide questions
ADVERTISEMENT

Find more quizzes from top tags

general knowledge
3615 Quizzes
119858 Questions
 technology
307 Quizzes
36705 Questions
 sports
963 Quizzes
19148 Questions
 history
1187 Quizzes
13475 Questions
 physics
598 Quizzes
13441 Questions
 biology
1160 Quizzes
12174 Questions
 science & technology
551 Quizzes
11015 Questions
 chemistry
490 Quizzes
9892 Questions
 maths
518 Quizzes
9324 Questions
 softskills
0 Quizzes
7131 Questions