Quick Revision: Thermodynamics | Physical Chemistry for NEET PDF Download

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EXTENSIVE AND INTENSIVE VARIABLES
(a) Extensive property of a system are those whose magnitude depends on the amount of matter present
in the system. These are additive in nature. For example, volume, internal energy, enthalpy, entropy, mass
etc. Sum, subtraction and multiplication of two extensive property is extensive.
(b) The property whose magnitude does not depend upon quantity of matter present in a system is known
as intensive property of the system. It is not an additive property. Examples are : temperature, pressure,
density etc. Sum, subtraction, multiplication division of two intensive properties is intensive.
INTERNAL ENERGY (U)
It is the energy associated with a system by virtue of its molecular constitution and motion of its molecule.
Such motion may be translational, rotational, vibrational etc.
Internal energy is a state function and an extensive property.
Heat supplied to system is denoted by q.
(1) When q > 0, heat has been supplied to system.
(2) When q < 0, system has rejected heat.
(3) When q = 0, no heat exchange ; process is adiabatic.
Work done on system (W)
(1) When W > 0 work is done on system.
(2) When W < 0 work is done by system.
Processes :
When a change is observed in the properties of system, a process is said to be taking place. This may be
a chemical reaction or a physical process, like crystallization. Processes are of two types.
(1) Reversible : No change in entropy of universe.
(2) Irreversible : Entropy of universe increases.