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 mercury” i.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 = 1.013
105N/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 celsius ” or “degree centigrade” which 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.