Class 9 science chapter 1 notes - Matter in our surroundings

                           Matter in our surroundings 

Index-

1. Introduction- What is the matter?

2. Physical nature of matter

3. Characteristics of particles of matter

4. States of matter 

5. Change in the state of matter  

• Effect of change of matter
• Effect of change of pressure        

6. Evaporation

7. FAQ    

Introduction-

 

Q. What is the matter?

Ans. Everything around us in this universe is made up of " material"  which is called matter. 

         Matter word comes from "material". For eg. a chair, book, cold drink, clouds, humans, etc.

         Or in other words -Anything occupies some " mass" and "volume".  

Note- matter can be living or non-living

So, matter is present everywhere so that's the name of the chapter matter in our surroundings.   

History- In ancient times, early Indian philosophers classified matter as up of 5 essential elements called " "Panch tatva"

1. Sky (Aakash)
2. Earth ( Prithvi)
3. Fire ( Agni) 
4. Air ( hava)
5. Water ( Jal)

 After that ancient Greek philosophers arrived at a similar classification of matter.  

Modern-day scientists have developed two types of classification of matter based on their physical properties and chemical properties.

Physical properties- properties that are physically seen through our eyes. for eg shape, size, weight, etc.

Chemical properties- property of a substance to undergo a specific chemical change.

Physical nature of matter-

 

• Matter is made up of particles.
• Particles of matter are further divisible into smaller and smaller particles on dilution.

Activity

• Take 2- 3 crystals of potassium permanganate and dissolve in 100 mL of water.
• Take out approximately 10mL of this solution and put it into 90 mL of clear water taking another beaker.
• Take out 10 mL of this solution and put in another 90 mL of clear water.
• Keep on diluting the solution this way 5 to 8 times.
• Is the water still colored?

   

Characteristics of particles of matter -

1.  Particles of matter have space between them. For eg. when we dissolve salt in water, the particles of salt get into the spaces between the particles of water.
2.  Particles of matter are in continuous motion. For eg. when a stylish student has lots of strong deodorants sprayed on his body just entered the classroom the smell of the deodorant reaches the students sitting on the last bench. 
3. Particles of matter attract each other.

States of Matter-

Due to the difference in the arrangement of particles of matter or we can say that due to the variation in the characteristics of the particles of matter the state around us exists in 3 forms-

Solid state 

Liquid state

Gaseous state

Q. Can matter change its state?

    

Changes in the state of the matter-

There are 2 ways by which we can change the state of matter-

• Change of temperature
• Change of pressure

  Effect of change of temperature-

   By changing the temperature we can change the state of matter i.e. from solid to liquid, liquid to gas, and vice-versa

  Activity-

• Take about 150 g of ice in a beaker and hang a laboratory thermometer through an iron stand in such a way that its bulb(end) is in contact with the ice.
• Start heating the beaker.
• Observe the temperature when the ice starts melting.
• Observe the temperature when all the ice has converted into water.
• Now, put a glass rod in the beaker and heat on a high flame while stirring till the water starts boiling.
• Keep an eye on the thermometer reading carefully till most of the water has vapourised.

   Explanation- On increasing the temperature of solids, results in increasing the kinetic energy of the particles. Due to the increase in kinetic energy, the particles start vibrating and start to move freely leaving their fixed positions. A stage is reached when the solids melt and are converted to liquid.

The minimum constant temperature at which a solid starts to melt to become liquid at the atmospheric pressure is called its melting point.

Q. When a solid, melts, its temperature remains constant so where does the heat energy go? 

 Ans. The temperature of the system does not change after the melting point is reached, till all the ice melts.

 So the extra amount of heat is used in changing the state by overcoming the force of attraction between the particles. As this energy is absorbed by ice without showing any temperature rise it is considered that heat hidden in the contents of the beaker is called latent heat of fusion.

When we continuously supply heat energy to water particles start vibrating even at a faster speed thereby, breaking the force of attraction of each other and moving freely.

At a certain temperature the liquid starts to change into gas at atmospheric pressure is known as its boiling point.

The heat required to change 1 kg of water into vapor at a boiling point is called latent heat vaporization.

Q. Is it possible to convert a solid into a gaseous state without changing into a liquid state?

Ans. Yes, it is possible through the sublimation process.

Activity-

• Take some camphor. After crushing it put it in a china dish.
• Put an inverted funnel and place it over the china dish. 
• Put a cotton plug on the opening of the funnel.
• Now, heat slowly and observe.
• What did you notice in this activity?

Explanation- On heating the china dish the solid camphor present inside the funnel starts to convert into camphor vapors. When inside the funnel temperature decreases camphor vapors start to convert into solid camphor and get deposited on the margins of the funnel.

Sublimation- Conversion of solid into gas directly without changing into the liquid state.

Effect of change of pressure-

On applying the pressure we can change the state of matter. Because, as we use pressure matter gets closer to each other and starts to interact, thereby increasing in force of attraction 

.

Some definitions-

  

   1. Fusion/ Melting - the process of conversion of a solid state into a liquid state on heating at its melting point is called fusion or melting. For eg. ice cream melts quickly in summer. 

  2. Solidification/ Freezing- the process of conversion of a liquid state into a solid state at its freezing point is called solidification/ freezing. For eg. ice cubes in a freezer.

  3. Vaporisation-  conversion of liquid into a vapor state at its boiling point. For eg. steam produce while making tea.

  4. Condensation- conversion of vapor into the liquid state. For eg. rain from a cloud. 

  5. Sublimation-  conversion of solid into gas. For eg. Camphor. 

  

  6. Deposition- conversion of gas into solid For eg. Hail.

Q. Do we always need to heat or change pressure to change the state of matter?

Q. Is there any other alternative to it?

Ans. Yes, when water, left uncovered, slowly changes into a vapor. For eg. wet clothes dry up.

Evaporation- 

The surface of liquid changes into vapors at any temperature below its boiling point is called evaporation.

NOTE- Evaporation is a surface phenomenon.

Factors affecting evaporation-

• Increase in surface area.
• Increase in temperature.
• A decrease in humidity.
• An increase in wind speed.

FAQ

Q. Why it is preferred to wear cotton clothes in summer?

Ans. During summer, evaporation of the particles at the surface of the liquid gain energy from the surroundings and change into vapor so to balance the lost energy the heat is absorbed from the body leaving the body cool.

Q. What are the characteristics of the particles of matter?

Ans. Characteristics of particles of matter-

• Particles of matter have space between them. 
• Particles of matter are in continuous motion.
• Particles of matter attract each other.

Q. Why gas fills completely the vessel in which it is kept?

Ans. Because gases have negligible force of attraction a gas is constantly moving with a high speed in all directions and due to this reason gas completely fills the vessel in which it is kept.

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