Class 9 Chemistry

Class 9 Chemistry

Class 9 chemistry is part of the class 9 science syllabus. The chemistry portion of the class 9 science syllabus includes the following chapters, Matter in Our Surroundings, Is Matter Pure Around us, Atoms and Molecules, and Structure of Atom. Four chapters comprise the class chemistry syllabus. One of the most important chapters of class 9 chemistry is Is Matter Around Us

Examples

Question 1

What is a physical change?

Solution 1

A physical change is a temporary change in which no new substance is formed and the composition or identity of the substance is not altered although certain specific physical properties may be changed.

Question 2

What is a   chemical change?

Solution 2

A chemical change is a permanent change in which the original substance gives rise to one or more substances with different properties.

Question 3

Indicate which of the following statements are true and which are false.

(a) A change, whether physical or chemical is always permanent.

(b) Photosynthesis in plants is a physical change.

(c) The mass of a substance does not change on burning.

(d) Carbohydrates burn in air to give carbon and water.

(e) A chemical change is always accompanied by the evolution or absorption of heat.

Solution 3

(a) False

(b) False

(c) False

(d) False

(e) True

Question 4 

What is the difference between physical and chemical changes?

Solution 4: 

Differences Between Physical and Chemical Change

Physical Change

Chemical Change

When a substance undergoes a physical change, its composition remains the same despite its molecules being rearranged.

When a substance undergoes a chemical change, its molecular composition is changed entirely. Thus, chemical changes involve the formation of new substances.

Physical change is a temporary change.

A chemical change is a permanent change.

A Physical change affects only physical properties i.e. shape, size, etc.

Chemical change both physical and chemical properties of the substance including its composition

A physical change involves very little to no absorption of energy.

During a chemical reaction, absorption and evolution of energy take place.

Some examples of physical change are freezing of water, melting of wax, boiling of water, etc.

A few examples of chemical change are digestion of food, burning of coal, rusting, etc.

Generally, physical changes do not involve the production of energy.

Chemical changes usually involve the production of energy (which can be in the form of heat, light, sound, etc.)

In a physical change, no new substance is formed.

A chemical change is always accompanied by one or more new substance(s).

Physical change is easily reversible i.e original substance can be recovered.

Chemical changes are irreversible i.e. original substances cannot be recovered.

 

Question 5: Which of the following is a chemical change? (a) Growth of a plant (b) Rusting of iron (c) Mixing of iron filings and sand (d) Cooking of food (e) Digestion of food (f) Freezing of water (g) Burning of a candle.

Solution 5: 

If the chemical composition is changing, then it is a chemical change, and if the chemical composition is remaining the same, then it is a physical change.

Growth of a plant, rusting of iron, cooking of food, digestion of food, and burning the candle are chemical changes because here is the chemical composition of the substance changes.

 

Question 6: Which of the following is not a chemical change? a) Formation of curd b) ripening of banana c) corrosion of iron d) melting of wax​

 

Solution 6:  Melting of wax is not a chemical change.

Option (d).

Explanation:

  • Mainly there are two types of changes which are chemical and Physical.
  • Such changes in which a new substance is formed from a substance and which can’t be reversed are known as the Chemical changes.
  • Among the given options Formation of Curd,  Ripening of banana and Corrosion of iron are examples of a chemical reaction as each of these changes can not be reversed, whereas melting of wax is a physical change as in this there is only change in the physical state , no new substance is formed.

 

Practice Questions

  1. What is the difference between physical and chemical changes?

  2. Which of the following is a chemical change? A. Boiling of water B. Boiling of egg C. Burning of paper D. Burning of cloth

  3. Which of the following is a chemical change?
  1. growth of a plant
  2. rusting of iron
  3. mixing of iron filings and sand
  4. cooking of food
  5. digestion of food
  6. freezing of water
  7. burning of a candle

  1. The property of flow is unique to fluids. Which one of the following statements is correct?

(a) Only gases behave like fluids

(b) Gases and solids behave like fluids

(c) Gases and liquids behave like fluids

(d) Only liquids are fluids

  1. The boiling point of water at sea level is
    1. 0°C
    2. 273 K
    3. 373 K
    4. 273°C

  2. Which of the following is not a chemical change? 
  1. Burning of fuels
  2. Rusting of Iron
  3. Drying of clothes
  4. Formation of curd from milk

  1. At room temperature the forces of attraction between the particles of solid substances are ………….. than those which exist in the gaseous state.

  2. Which of the following is not a chemical change?

(A) Sublimation

(B) Combustion

(C) Electrolysis

(D) Rusting

  1. Give some chemical change examples. 

Pure? In this chapter, we learn about many things, including the difference between physical and chemical changes.

 

Study Material

  1. Difference Between Physical And Chemical Change

    We encounter a lot of changes in our surroundings day to day that which we may not necessarily notice. For instance, melting of wax, rusting of iron, bread turning into toast and more. All of these changes are physical changes or chemical changes. Thus, in this article, we will study the difference between physical and chemical change. Physical change is when the physical traits of a substance changes. Moreover, it does not make any internal changes. Whereas, a chemical change is when the internal structure gets affected by a substance and forms a new substance.

    Changes in energy are always accompanied by a particular chemical change or physical change.  Many changes happen in a natural environment such as evaporation of water, condensation, rainfall, etc. The change in state is involved in all these changes. During some reaction, the old bonds in the reactants break and new bonds are created in the products.

  2. What is Chemical Change?

  • The change in which the molecular composition is completely altered and a new product is formed is called a chemical change.
  • Chemical changes create a new product.
  • Chemical changes are irreversible and permanent.
  • It reveals that chemical change cannot be reversed by changing or altering the experimental changes.
  • The mass of the substance is altered during a chemical change. Either the mass is added or removed.
  • During a chemical change, the energy changes occur. There is an energy difference in the breaking of old bonds in reactants and the formation of new bonds in products.
  • The reaction is called an exothermic reaction if the energy is released and as an endothermic reaction when the energy is absorbed.

Examples of Chemical Change

  1. Burning of wood or paper
  2. Burning of camphor
  3. Souring of milk
  4. Burning of candle
  5. Digestion of food

There is a difference in energy during the breaking and making of bonds. The energy is given out to the surroundings if the energy required to break the bonds is higher than the energy required to make the bonds.

These changes or reactions are called exothermic. But, the energy is absorbed from the environment when the energy needed to break the bond is lower than the energy required to make the bonds. Such reactions are called endothermic reactions.

  1. What is Physical Change?
  • During physical change, the arrangement of molecules is altered leading to change in state. No new products are formed, and the molecular composition remains totally the same.  For example, the molecular composition of ice and water is not altered.
  • No energy changes occur when as a result of a physical change. The energy needed to bring a physical change is equal to the amount of energy required to reverse the change. There is no change in energy.
  • The changes are reversible and temporary. The reaction gets reversed if the cause of producing the change is removed. For example, water on freezing forms ice and ice on melting forms water.
  • During the physical change, the mass of the substance remains the same. Only energy is added or removed, and mass is not involved in a physical change.

Examples of Physical Change

  1. Dissolution of sugar in water
  2. Melting of ice
  3. Freezing of water
  4. Boiling of water
  5. Melting of wax

Difference between physical and chemical change:

There are many differences between physical and chemical changes and it is important to understand them to be able to understand these concepts clearly. The comparison and difference between physical and chemical changes are given below along with their examples.

Physical change

Chemical change

Only physical changes like odour, physical state, density, volume etc. changed and chemical properties remain unchanged

The chemical composition and chemical properties undergo a change

No new substance is formed in a physical change.

A new substance is formed in a physical change.

Very little or no energy in the form of heat, light or sound is usually absorbed or given out in a physical change

A chemical change is always accompanied by absorption or evolution of energy

It is a temporary change

It is a permanent change

The original form of substance can be regained by simple physical method

Original substance cannot be obtained by simple physical method

It is reversible

It is irreversible

 

Videos (3)

Examples

Q1 .What is a physical change?

Solution:

A physical change is a temporary change in which no new substance is formed and the composition or identity of the substance is not altered although certain specific physical properties may be changed.

Q2. What is a chemical change?

Solution:

A chemical change is a permanent change in which the original substance gives rise to one or more substances with different properties.

Q3.: What is the difference between physical and chemical changes?

Solution:

Physical Change

Chemical Change

When a substance undergoes a physical change, its composition remains the same despite its molecules being rearranged.

When a substance undergoes a chemical change, its molecular composition is changed entirely. Thus, chemical changes involve the formation of new substances.

Physical change is a temporary change.

A chemical change is a permanent change.

A Physical change affects only physical properties i.e. shape, size, etc.

Chemical change both physical and chemical properties of the substance including its composition

A physical change involves very little to no absorption of energy.

During a chemical reaction, absorption and evolution of energy take place.

Q4 .Which of the following is a chemical change? (a) Growth of a plant (b) Rusting of iron (c) Mixing of iron filings and sand (d) Cooking of food (e) Digestion of food (f) Freezing of water (g) Burning of a candle.

Solution:

If the chemical composition is changing, then it is a chemical change, and if the chemical composition is remaining the same, then it is a physical change.

Growth of a plant, rusting of iron, cooking of food, digestion of food, and burning the candle are chemical changes because here is the chemical composition of the substance changes.

Q5. Which of the following is not a chemical change? a) Formation of curd b) ripening of banana c) corrosion of iron d) melting of wax​

Solution:

Option (d).

Explanation:

  • Mainly there are two types of changes which are chemical and Physical.
  • Such changes in which a new substance is formed from a substance and which can’t be reversed are known as the Chemical changes.
  • Among the given options Formation of Curd,  Ripening of banana and Corrosion of iron are examples of a chemical reaction as each of these changes can not be reversed, whereas melting of wax is a physical change as in this there is only change in the physical state , no new substance is formed.

Practice Questions

Chemistry Class 9 Practice Questions

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1 / 6

Which is not a Types of Chemical Formulae

2 / 6

What is its chemical formula of Aluminium hydroxide formula ?

3 / 6

Atom is defeined as

4 / 6

What are Atoms made of

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What is the atomic number of Helium

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What is the Atomic masses of Chlorine

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Related Study Materials

FAQ

Definition of Physical Change:

Physical change is the kind of change where the matter switches into another form. In here, the chemical properties do not change. For instance, when you tear a paper, it will only change its shape and size. However, the properties will be the same. Similarly, when water turns into ice or vapour, the chemical properties remain the same, only the physical state changes. Thus, this will help you in understanding the difference between physical and chemical change better. A physical change does not bring any alternation of any kind on the chemical properties. Moreover, the changes are usually reversible and temporary.

Definition of Chemical Change

A chemical change is the exact opposite of physical change. It results in a new product after the reaction. For instance, when you burn a piece of paper or wood, it will change into ash. Thus, there is a change in the composition of the material forming a new product. In other words, chemical changes do alter the properties of a substance throughout the reaction. It is because the atoms plus molecules of the substances start rearranging themselves to form a new product. Moreover, these changes are not easily reversible, in fact, they are irreversible. So, it is a permanent change which alters the melting point, taste, colour and more.

Name the process which occurs when a drop of dettol is added to water.


When dettol is added to water, diffusion takes place.

To which physical state of matter do the following statements apply?

(i) Incompressible, no fixed shape

(ii) Compressible, no definite volume

(iii) Liquid

(iV) Gas

What are some chemical change examples?

 

Some chemical change examples are, burning, cooking, rusting, and rotting. Examples of physical changes are boiling, melting, freezing, and shredding.

   
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