Matter in Our Surroundings- Blog 3

Chapter 1: MATTER IN OUR SURROUNDINGS-III

Hello boys. GOOD MORNING!!!

Hope the previous blog was helpful and the queries are dealt with.

Today we will be looking at:

1. Interconversion of States of Matter
2. Effect of Temperature on Matter
3. Latent Heat

By the end of this topic, the learner will be able to:

1. Understand the effect of temperature and pressure on interconversion of matter
2. Define Sublimation
3. Describe Latent Heat of Fusion and Vapourization.

So let us all start our topic for today......

INTERCONVERSION OF STATES OF MATTER

The phenomenon of change from one state of matter to another and back to the original state is known as Interconversion of states of matter.

It is the effect of change of the following conditions:

1.     Changing the temperature.

2.     Increasing or decreasing pressure

3.     Changing both temperature and pressure.

TEMPERATURE is inversely proportional to PRESSURE. ( If temperature increases pressure will decrease and if temperature decreases pressure will increase)

Example: Colder places have low temperature but high pressure.

Changing the Temperature of Matter:

On increasing the temperature of solids, the kinetic energy of the particles increases. Due to the increase in kinetic energy, the particles start vibrating with greater speed. The energy supplied by heat overcomes the forces of attraction between the particles. The particles leave their fixed positions and start moving more freely. A stage is reached when the solid melts and is converted to a liquid.

(i) Interconversion of solid into liquid and melting: The solid can be converted into liquids by heating them. Similarly liquids can be cooled to form solids.

e.g.: Ice at 0℃ changes into water at 0℃ (273 K), when heat energy is supplied to it. The water at 0℃ changes into ice at 0℃ on freezing.

(0℃ = 273 K) REMEMBER!!!

(100℃ = 100+273 = 373 K)

Q. Convert the following temperatures to the Celsius scale:
(a)           293 K                               (b)         470K
(a) 293K = (293 - 273) = 20 degree Celcius
(b) 470K = (470 - 273) = 197 degree Celcius

Q. Convert the following temperature to the Kelvin scale:
(a)   25degree celsius                 (b) 373 degree celsius
(a) 25 degree Celsius = (25 + 273) = 298 Kelvin
(b) 373 degree Celsius = ( 373 + 273) = 646 kelvin

• MELTING OR FUSION: The minimum temperature at which a solid melts to become a liquid at the atmospheric pressure is called its melting point. 

NOTE: The melting point of a solid is an indication of the strength of the force of attraction between particles.

• FREEZING OR SOLIDIFICATION: The process due to which a liquid changes into solid state by giving out heat energy is called freezing or solidification.

EXPLANATION: On increasing the temperature of solids, the K.E. of particles increases. Due to increase in K.E. the particles start vibrating with greater speed. The energy supplied overcomes the forces of attraction between the particles. Then, the particles leave there fixed positions and start moving freely. Thus, the solid melts.

LATENT HEAT: The amount of heat required to change the state of matter from one state to another without the rise in temperature is know as Latent heat of that Substance.

Latent Heat is of Two types:

1. LATENT HEAT OF FUSION: The amount of heat required to change the state of matter from SOLID state to LIQUID state without rise in temperature at its MELTING point is known as latent heat of FUSION.

MELTING POINT: The Temperature at which a SOLID changes into LIQUID state by absorbing heat at atmospheric pressure is called MELTING point. E.g. ICE melts at 0℃.

FREEZING POINT: The constant temperature at which a liquid changes into solid state by giving out heat energy is called freezing point. e.g. WATER freezes at 0℃

The numerical value of freezing point and melting point is same. Melting point of ice= Freezing point of water=0℃(273.16 K)

2. LATENT HEAT OF VAPORIZATION: The amount of heat required to change the state of matter from LIQUID state to GASEOUS state without rise in temperature at its BOILING point is known as latent heat of VAPORIZATION.

Liquid into Gas/ Gas into Liquid: Liquids can be converted into Gases by heating. Similarly, Gases can be converted into Liquid by cooling them. e.g. Water changes into Gas at 100℃/absorbing heat. Steam changes back into water at 100℃ by giving out this energy.

BOILING or VAPORIZATION: The process in which Liquid changes into Gaseous state by absorbing heat energy is known as boiling.

BOILING POINT: The Temperature at which a liquid changes into Gaseous state by absorbing heat at atmospheric pressure is called boiling point. e.g. Water boils at 100℃.

CONDENSATION: The process in which Gas changes into liquid state by giving out energy is called condensation.

CONDENSATION POINT: The temperature at which gas changes into liquid state by giving out heat at atmospheric pressure is called condensation point. e.g. Steam changes into water at 100℃. 

EXPLANATION: When heat is supplied to water, the particle start moving faster. At a certain temperature, a point is reached when the particles have enough energy to break the forces of attraction between the particles. At this temperature the liquid start changing into gas.

Q. Why does the temperature of a substance remain constant during its melting point or boiling point?
A. The temperature of a substance remains constant at its melting and boiling points until all the substance melts or boils because, the heat supplied is continuously used up in changing the state of the substance by overcoming the forces of attraction between the particles. This heat energy absorbed without showing any rise in temperature is givne the name latent heat of fusion/latent heat of vaporisation.

Q.Why is ice at 273K more effective in cooling than water at the same temperature?
A. The ice at 273 K is more effective in cooling than water because particles in ice at 273 K have less energy as compared to particles in water at the same temperature.

Q What causes more severe burns- boiling water or steam?
A When water changes to steam, it absorbs latent heat of vapourisation. Thus, steam contains more heat than boiling water. So, steam causes more severe burns as compared to boiling water.

DIRECT INTERCONVERSION OF SOLID INTO GASEOUS STATE:

SUBLIMATION: The process of conversion of SOLIDS into GASEOUS state without undergoing the LIQUID phase at room temperature. E.g. Naphthalene balls disappear in air

over time.This process is called SUBLIMATION.

DEMONSTRATION OF SUBLIMATION: 

The solid AMMONIUM CHLORIDE on providing heat changes directly into vapours without undergoing the liquid state. You will understand the process well in the following video.

https://www.youtube.com/watch?v=WzqnfS0-uFk 

(You may stop at 6:21 min)

WHAT WE DID TODAY!

LET'S SUMMARIZE

BY INCREASING THE TEMPERATURE (DECREASING PRESSURE):

1. SOLID----------> LIQUID :- The process is called MELTING.

2. LIQUID---------> GAS :- The process is called VAPORIZATION.

BY DECREASING THE TEMPERATURE (INCREASING PRESSURE):

3. GAS-------------> LIQUID :- The process is called CONDENSATION.

4. LIQUID-----------> SOLID :- The process is called FREEZING OR SOLIDIFICATION.

5. SOLID----------->GAS :- SUBLIMATION

6. GAS-------------> SOLID :- SUBLIMATION

Home Assignment 
1.Do Q No 1,2,3,4,5,6,78,9  of NCERT page12
2.
This is all today.

See you tomorrow.

BYE!