# Introduction

## States of Matter of Class 11

Matter can be classified into three categories depending upon its physical state namely solid, liquid and gaseous states. Solids have a definite volume and shape; liquids also have a definite volume but no definite shape; gases have neither a definite volume nor a definite shape.

### DISTINCTION BETWEEN THREE STATES OF MATTER

 Sl. No. Solids Liquids Gases 1. Particles are very Closely packed Particles are loosely packed Particles are very loosely packed 2. Voids are extremely small Voids are relatively larger Voids are very large 3. Inter particle forces are large Inter particle forces are intermediate Intermediate forces are negligible 4. Particle motion is restricted to vibratory motion. Particle motion is very slow Particle motion is very rapid and also random.

### MEASURABLE PROPERTIES OF GASES

Mass, volume, temperature are the important measurable properties of gases.

• Mass: The mass of the gas is related to the number of moles as

n = w/M

Where n = number of moles

w = mass of gas in grams

M = molecular mass of the gas

• Volume: Since gases occupy the entire space available to them, therefore the gas volume means the volume of the container in which the gas is enclosed.

Units of Volume: Volume is generally expressed in litre or cm3 or dm3 1m3 = 103 litre
= 103 dm3 = 106 cm3.

• Pressure: The force exerted by the gas per unit area on the walls of the container is equal to its pressure.

Units of Pressure: The pressure of a gas is expressed in atm, Pa, Nm–2, bar or,
lb/In2 (psi).

760 mm = 1 atm = 10132.5 KPa = 101325 Pa = 101325 Nm–2

760 mm of Hg = 1.01325 bar = 1013.25 milli bar = 14.7 lb/2n2 (psi)

• Temperature: Temperature is defined as the degree of hotness. The SI unit of temperature is Kelvin. On the Celsius scale water freezes at 0°C and boils at 100°C where as in the Kelvin scale water freezes at 273 K and boils at 373 K.