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SUBJECT-CHEMISTRY

CHAPTER-STATES OF MATTER

SUB TOPIC-LIQUID STATE, VAPOUR PRESSURE, SURFACE TENSION, VISCOSITY

KEY NOTES:
 VAPOUR PRESSURE:
The pressure exerted by the vapour of the liquid over the surface of the liquid is called
vapour pressure.
FACTORS AFFECTING VAPOUR PRESSURE:

(i) Vapour Pressure α Temperature

(ii) Vapour Pressure depends on nature of liquid. Liquids having weak force of attraction have
more vapour pressures.

 NORMAL BOILING POINT- At 1 atm pressure, the boiling point is called as normal boiling
Point.
 STANDARD BOILING POINT- At 1 bar pressure, the boiling point is called as standard boiling
Point.

 SURFACE TENSION:
It is defined as the force per unit length acting perpendicular to the line drawn on the plane of
the surface.
UNIT OF SURFACE TENSION- N/m or dyne/cm

FACTORS AFFECTING SURFACE TENSION:

(i) Surface tensionα1/Temp
(ii) Liquids having strong force of attraction have more surface tension.

CONSEQUENCES OF SURFACE TENSION:

(i) Small drops of liquids are spherical in shape.

(ii) Liquid rises in the capillary tube.

 VISCOSITY:
It is a measure of resistance to the flow which arises due to the internal resistance between the
layers of the liquid.

COEFFICIENT OF VISCOSITY:(ƞ)

It is defined as the viscous force when velocity gradient is unity and area of contact is one unit.
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SI Unit of coefficient of viscosity is Nsm or Pa.s