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Class 9, Science, Chapter-1, Lecture-1, States of Matter (Notes)

Matter:

Something which has mass, occupies space and can be sensed is called matter.

Characteristics of Matter:

  1. Matter is composed of particles
  2. The particles of matters are very small
  3. The particles of matter have space between them
  4. The particles of matter are in constant motion
  5. The particles of matter attract each other

Density:

The mass per unit volume of a substance is termed as its density
Mathematically, ${\rm{d = }}{{\rm{m}} \over {\rm{v}}}$

Where, d = density
             m = mass
             v = volume
Density is a SCALAR
S.I. unit is ${\rm{kg}}{{\rm{m}}^{{\rm{ - 3}}}}$
Commonly used unit is ${\rm{g}}{\left( {{\rm{cm}}} \right)^{{\rm{ - 3}}}}$ or ${\rm{g}}{\left( {{\rm{mL}}} \right)^{{\rm{ - 1}}}}$${1c{m^3} = 1mL}$

Diffusion:

The intermixing of particles of two different substances on their own is called diffusion.

Osmosis:

The movement of solvent molecules through a semi-permeable membrane into a region of higher solute concentration, to equalize the solute concentrations on the two sides is termed as osmosis.

Osmosis is a special kind of diffusion:

Justification:
During diffusion, particles of different substances (solute and solvent) move and intermix to make the concentration homogeneous.
During osmosis, only the solvent particles move through a semi permeable membrane from lower solute concentration to equalize the concentration on both sides.
So, osmosis is a special kind of diffusion.

Cohesion:

The force of attraction by which the particles of a matter are bound to one another is termed as cohesion.

Classification of Matter: (on the basis of physical state)

  1. Zero state (Bose-Einstein Condensate: BEC)
  2. Solid
  3. Liquid
  4. Gas
  5. Plasma
  6. Beam
  7. Wave

Change of State:

Example of Co-existence of Solid-Liquid-Gaseous state:

Water exists in all the three states at temperature 0.01 0C and at pressure 4.58 mm of Hg

Melting (Fusion):

The process in which a matter changes its state from solid to liquid at a fixed temperature without any change in its temperature is termed as melting or fusion.

Melting Point:

The fixed temperature at which a solid melts to become a liquid at atmospheric pressure (760 mm of Hg) is called its melting point.

Latent heat of fusion:

The amount of heat (energy) required in converting unit mass of a solid into liquid at a given temperature and pressure without any change in temperature of the substance is called the latent heat of fusion of the substance.

  • S.I. unit is J kg-1.

The Latent heat of fusion of ice at 0 OC and 1 atmospheric pressure is 334 kJg–1:

Meaning: The quantity of heat required to convert 1 g of ice into water at 0 OC and 1 atmospheric pressure without any change in temperature is 334 kJ.