# CBSE Chemistry :Matter – Nature and Behavior – Important Terms

## Matter – Nature and Behavior – Important Terms

### Density:

The mass per unit volume of a substance is called density.

### Kinetic Energy (K.E.):

The energy possessed by a particle by virtue of its motion is called kinetic energy Kinetic energy of particles in solid state is very less.

### Pressure:

The force per unit area is called pressure.

### Units of pressure:

The common unit of pressure is millimeter of mercuryi.e., mm of mercury (mm-Hg) or just mm.

The mm of mercury pressure is also called torr.

1 torr = 1mm Hg

Another common unit of pressure is Atmosphere.

1 Atmosphere is that pressure which supports a column of mercury 760 mm Hg at 0°C at sea level.

1 atmosphere = 760 mm Hg

The S.I. Unit of pressure is pascal (Pa).

1 atm = 1.013105N/m2

= 1.013xl05 Pa

Another unit of pressure used is bar. It has been derived from S.I. Unit of pressure.

1 bar =105 N/m2

1 atm=1.013 bar

### Unit of volume

: The S.I. unit of volume is “cubic meter” which is written as m3.

l m3=106 cm3·

### Temperature of a gas:

The molecules of a gas are in motion and posses kinetic energy. Therefore, the temperature of a gas is an indication of the average kinetic energy of gas molecules.·

### Units of temperature:

The common unit of temperature is degree celsiusor degree centigradewhich is written as

°C.

The S.I. unit of temperature is Kelvin which is denoted as K (letter K).

0°C = 273.16K

### Melting point of solid:

The constant temperature at which a solid changes to a liquid is called its melting point. Melting point of ice is 0°C or 273.16 K.

Melting point of a solid is an indication of the strength of the intermolecular forces of attraction.·

### Latent heat of fusion:

The amount of heat energy that is required to change 1 kg of a solid into a liquid at atmospheric pressure without any change of temperature at its melting point is known as Latent heat of fusion.·

### Boiling point:

The constant temperature at which a liquid changes into gas/vapour is known as its boiling point. Boiling point of water is 100°C or (273 + 100) = 373 K.·

### Latent heat of vapourisation:

The amount of heat energy that is required to change 1 kg of a liquid into gaseous state at atmospheric pressure without any change of temperature at its boiling point is known as Latent heat of vapourisation.

· The smallest particle of an element is called an atom, i.e., matter is made up of particles.·

#### Atom:

The smallest particle of an element that may or may not have physical existence is called atom.·

#### Diffusion:

This is the process of intermixing of particles of two substances on their own. On heating the process of diffusion increases.·

#### Standard Temperature and Pressure (S.T.P.)

Standard Temperature = 0°C or 273 K

[t°C = (273 + t) K]

Standard Pressure = 1 atmosphere = 760 mm of Hg.