Matter in Our Surroundings- Blog 4

CLASS 9 CH-1 MATTER IN OUR SURROUNDINGS-IV

CHEMISTRY

Chapter 1: MATTER IN OUR SURROUNDINGS-IV

Hello boys!!! Hope you all are doing well today. 

Let us begin the class.

Today we will be looking at:

1. Effect of Pressure on Matter.
2. The process of Evaporation.
3. The factors affecting Evaporation.

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

1. Understand the effect of pressure on inter-conversion of matter.
2. Define Evaporation.
3. Describe the effect of temperature, pressure, surface area and humidity on Evaporation.

INTER-CONVERSION OF STATES OF MATTER

EFFECT OF CHANGE OF PRESSURE

The various states of matter (i.e. solid, liquid, gas) is due to the difference in the distances between the constituent particles. 

https://www.youtube.com/watch?v=WzqnfS0-uFk 
(You may begin from 6:22 min)

The effect of pressure on state of matter can be understood by the following experiment.

The above experiment shows that on applying pressure and reducing temperature gases can be liquefied as the particles come closer to each other.

A Gas can be liquefied by applying pressure or by lowering temperature.

CRITICAL TEMPERATURE: The minimum temperature below which a gas can be liquefied.

CRITICAL PRESSURE: The minimum pressure above which a gas can be liquefied.

EXPLANATION:

When the particles of fluid are present under low pressure, they are in gaseous state (Purple cylinder in the figure). When high pressure is applied, the particles come closer increasing the forces of attraction between the particles and it is converted into LIQUID (Orange cylinder in the figure). When more pressure is applied, ultimately the forces of attraction become so strong that the particles bind together tightly and change into SOLID.


e.g. Carbon dioxide gas is changed into solid Carbon dioxide by applying pressure. Dry ice is the solid form of carbon dioxide. It is used primarily as a cooling agent. It is Carbon dioxide stored at high pressure.

LPG AND CNG are filled into cylinders by applying pressure (Liquification of Gas).

Attempt the In-text questions on page no. 9
Comment your doubts, if any in the comment box.

Let us move further.....

Boys, have ever noticed that water left uncovered slowly changes into vapour. You must have observed that wet clothes dry up. 

Do we always need to heat or change pressure for changing the state of matter?

This is happening because of the phenomenon -EVAPORATION.

The process of liquid changing into vapours even below its boiling point is called as evaporation.

EXPLANATION: The particles of matter are always moving and are never at rest. At a given temperature in any gas, liquid or solid, there are particles with different amounts of kinetic energy. In the case of liquids, a small fraction of particles at the surface, having higher kinetic energy, is able to break away from the forces of attraction of other particles and gets converted into vapour.

NOTE: Evaporation is a surface phenomena whereas boiling is a bulk phenomena.

FACTORS AFFECTING EVAPORATION

Refer Activity 1.14 page 9 of text book
The rate of evaporation depends upon following factors:

1) TemperatureThe rate of evaporation increases on increasing temperature of the liquid. With the increase of temperature, more number of particles get enough kinetic energy to go into the vapour state.

https://www.youtube.com/watch?v=Kh9T26Ze-Xk

2)Humidity of air
The amount of water vapours present in air is called humidity.
When the amount of water vapours present in the air is small it is called dry air.
When the amount of water vapours present in air is large it appears to be damp.
When the humidity of air is low, then the rate of evaporation is high,and water evaporates more readily.
When the humidity of air is high, then the rate of evaporation is low and water evaporates very slowly.

https://www.youtube.com/watch?v=gI7nuAUe-IM

3) Surface Area
The rate of evaporation increases on increasing the surface area of the liquid.

e.g. If the same liquid is kept in a test tube and in a china dish,then the liquid kept in the china dish evaporates more rapidly. We spread out the washed clothes while drying to increase their surface area for rapid evaporation of water present in them.

4) Wind Speed

The rate of evaporation of a liquid increases with the increasing wind speed.
https://www.youtube.com/watch?v=TD6CLHPbP3c

When the speed of wind increases, the particles of water vapours move away with the wind, decreasing the amount of water vapours in the surrounding. This increases the rate of evaporation of water.

The washed wet clothes dry more quickly on a windy day because evaporation is faster due to the high speed of the wind.

ASSIGNMENTS:

1. Do the in-text questions on page no. 9.
2. Read the textbook carefully.

BYE!

TAKE CARE.