## Sunday, May 24, 2015

### Ch.2 States of Matter - JEE Main Core Points for Revision

Importance of  Core Revision Points: Core Revision Points are important because if you remember them strongly, many more points related to them will come out of your memory and help you to answer question and problems. Read them many times and make sure you remember them very strongly.

Matter exists in three physical states, solid, liquid, and gaseous.

Solid State: A substance in solid state has a definite size (volume) and a definite shape. As we know shape can be changed by applying force. It can be broken into pieces by hammering etc. The solids are hard and rigid. Some common solids in article share we see are stainless plates and glasses. We also use things like combs, mirrors, scooters and cars. Some of the elements that we see in solid shape are iron, aluminium, silver,and gold etc.

Liquid State: A liquid possesses definite volume but not a definite shape.

Gaseous State: A gas of a given mass, neither possesses a definite volume nor definite shape.

Contents of the Chapter

2.1 Intermolecular Forces Versus Thermal Energy of Three States of Matter
2.2 Measurable Properties of Gases
2.3 Gas Laws
2.4 Some Problems Involing Chemical Equations

2.6 Kinetic Molecular Theory of Gases
2.7 Maxwell-Boltzmann Distribution of molecular Speeds
2.8 Deviations from Ideal Gas Behavior - Real Gases
2.9 Liquification of Gases and Their  Critical Phenomena
2.10 Kinetic Molecular Model of Liquids
2.11 Properties of Liquids
2.12 Charateristics of Solids
2.13 Classification of Solids
2.14 Size andShare of Crystals
2.15 Types of Solids on the basis of Binding Forces
2.16 Intermolecular Forces

## 2.1 Intermolecular Forces Versus Thermal Energy of Three States of Matter

Particle concept of matter: According to this concept, all matter consists of tiny particles (atoms or molecules) which are constantly moving in all directions. These particles exert attractive forces upon one another called inter particle (intermolecular) forces.

## 2.2 Measurable Properties of Gases

1. Measurement of Mass
2. Measurement Volume
3. Measurement of Pressure
4. Measurement of Temperature

## 2.3 Gas Laws

1. Boyle's Law (Boyle Bday 25 January)
2. Charles' Law
4. The Combined Gas Lawor Ideal Gas Equation
5. Dalton's Law of Partial Pressures
6. Graham's Law of Diffusion or Effusion

1. Boyle's Law
2. Charles' Law
4. The Combined Gas Law or Ideal Gas Equation

2.4 Some Problems Involing Chemical Equations

### 6. Graham's Law of Diffusion or Effusion

When a cylinder of colourless hydrogen gas inverted over a cylinder of brown bromine vapour, after some time, we can see that both the cylinders become yellowish brown. This means hydrogen has travelled to the lower cylinder and bromine vapour moved to the upper cylinder.

Gases have the tendency to intermix and to form a homogeneous mixture. This property is known as diffusion.

Diffusion is defined as the process of intermixing of two or more gases, irrespective of density relationship adn without the help of external agency.

Graham's Law of Diffusion: The rate of diffusion of a gas is inversely proportional to the square root of its density or molar mass.

Effusion: Effusion is a special case of diffusion wherein a gas escapes through a small aperture from the vessel in which it is contained.

The rate of escape is inversely proportional to the square root of its density or molar mass.

## 2.6 Kinetic Molecular Theory of Gases

The important postulates of the Kinetic Molecular Theory

1. Gases consist of large number of minute particles called molecules.
2. The molecules are separated by large distances. The empty space in gas is so large that the actual volume occupied by the molecules is negligible when compared to the total volume of the gas.
3. Molecules of the gas are in state of random motion in all directions. In this motion they keep on colliding with each other and also the walls of the container.
4. Collisions between molecules as well as between molecules and walls of the container are elastic. It means there is no loss of energy in the system due to collisions. There may be redistribution of energy among molecules.
5. There are no forces of attraction or repulsion between molecules.
6. The pressure exerted by a gas on the walls of a container is due to the collision of the molecules.
7. The average kinetic energy of translational motion of gas molecules is directly proportional to the absolute temperature of the gas.

2.7 Maxwell-Boltzmann Distribution of molecular Speeds

Average, root mean square and most probable velocities and their relation with temperature;

Molecular Speeds

From the expression for kinetic temperature

Substitution gives the root mean square (rms) molecular velocity:

From the Maxwell speed distribution this speed as well as the average and most probable speeds can be calculated.

http://hyperphysics.phy-astr.gsu.edu/Hbase/kinetic/kintem.html

## 2.8 Deviations from Ideal Gas Behavior - Real Gases

Van der Wals' equation for real gases

## 2.9 Liquification of Gases and Their  Critical Phenomena

Critical temperature is the temperature above which a gas cannot be liquefied however high the pressure may be.

2.10 Kinetic Molecular Model of Liquids

1. Liquids are composed of molecules.
2. There are appreciable intermolecular forces between molecules that hold them together in the liquid.
3. Still, the intermolecular forces are weak, hence molecules of liquids are in constant random motion.
4. The average kinetic energy of molecules in a given sample is proportional to the absolute temperature.

## 2.11 Properties of Liquids

1. Volume
2. Density
3.Compressibility
4. Diffusion
5. Evaporation
6. Enthalpy of vaporisastion

7.Vapour Pressure

When a liquid is placed in a vessel and is covered with jar, from the liquid evaporation takes place and the vapour of the liquid or molecules of the liquid in gap form fill the available space. As the evaporation takes place over a period of time, the number of gaseous molecules goes up. As evaporation is taking place some molecules in the gaseous phase collide with the surface of the liquid and become liquid molecules. Thus both evaporation and condensation take place simultaneously. But initially there is more evaporation and less condensation. At the some stage, rate of evaporation equals rate of condensation and equilibrium is established between gas and liquid phases. The pressure exerted by the vapours at the equilibrium stage is called vapour pressure.

Definition
The pressure exerted by the vapours above the liquid surface (in a closed vessel) in equilibrium with the liquid at a given temperature is called vapour pressure.

Vapour pressure changes from liquid to liquid. It depends on intermolecular forces. if the forces in a liquid are weak, there is more gas formation and hence more vapour pressure.

A higher temperature there is more gas formation and hence for the same liquid vapour pressures increase with temperature.

8. Boiling
9. Surface tension
10. Viscosity

## 2.12 Charateristics of Solids

1. Solids are rigid and have definite shape

## 2.13 Classification of Solids

1. Crystalline Solids  2. Amorphous Solids

## 2.14 Size and Share of Crystals

Law of constancy of interfacial angles of a crystal,

## 2.15 Types of Solids on the basis of Binding Forces

1. Molecular crystals
2. Iconic crystals
3. Covalent crystals
4. Metallic crystals

## 2.16 Intermolecular Forces

In addition to normal covalent bond, ionic bond, and metallic bond, there are weak attractive intermolecular forces which occur in all kinds of molecular solids. These are present in case of non-polar molecules such as H2, O2, CO2, CH4 etc. also.

These are classified as:
i) Dipole-dipole forces
ii) Dipole induced dipole forces
iii) Instantaneous dipole-instantaneous induced dipole forces (called London forces)
iv) Hydrogen bonding

#### 1 comment:

KVSSNrao said...

Updating the post.21 May is an important day in the life of Dedeepya.
Remembering her.