Thursday, April 24, 2008

Concept review Ch. 26 Laws of Thermodynamics

First law of thermodynamics

∆U = ∆Q -∆W

or ∆Q = ∆U + ∆W

In an ideal monatomic gas, the internal energy of the gas is simply translational kinetic energy of all its molecules.

the first law may be taken as a statement that there exists an internal energy function U that has a fixed value in a given state.

Remember that when work is done by the system,∆W is positive, If work is done on the system ∆W is negative.
When heat is given to the system ∆Q is positive. If heat is given by the system ∆Q is negative.

A positive ∆W decreases internal energy and a positive ∆Q increases internal energy.

Work done in an isothermal process on an ideal gas

W = nRTln(V2/V1)

Work done an isobaric process

W = p(V2-V1)

Work done an in isochoric process(volume of gas is constant)


Second law of thermodynamics

Kelvin-Planck statement

It is not possible to design a heat engine which works in cyclic process and whose only result is to take heat from a body at a single temperature and convert it completely into mechanical work.

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