Monday, August 25, 2008

Lwas of Thermodynamics - July Dec Revision

Zeroth Law of Thermodynamics

If a system A is in thermal equilibrium with a system C and if B is also in thermal equilibrium with system C, then A and B are in thermal equilibrium with each other whatever the composition of the systems.

First law of thermodynamics;

Energy cannot be created or destroyed.

Energy can neither be created or nor destroyed although it can be converted from one form into another.

The energy of a system that isolated from its surroundings is constant.

Mathematical expresson for the first law

ΔU = q + w
q = heat added to the sytem
w = work done on the system

Sign conventions for heat and work

When w and q are positive, the internal energy increases. It means that energy is supplied to the system.

When w and q are negative, the internal energy decreases. It means that energy has left the system.

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