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Charles’s Law and Kelvin Temperature
Charles’s observations led to the absolute (Kelvin) temperature scale,
since the gas, according to the equation, would have zero volume at –273
degrees C. The absolute temperature scale was defined by Kelvin so that
absolute temperature equals negative 273 degrees C and each absolute
degree is the same size as a Celsius degree. The modern value for absolute
zero is –273.15 degrees C. This temperature scale allows Charles’s Law to
be written V/T = Constant, where V is the volume of the gas, T is the
temperature on the absolute scale, and the constant depends on the
pressure and the amount of gas present.
In 1802, Joseph Gay-Lussac played around with the relationship between
pressure and temperature and came up with an equation a lot like
Charles’s Law: P/T = Constant.
Generalized Gas Law
We can combine Boyle’s, Charles’s, and Gay-Lussac’s Laws to express
this generalized gas Law: PV/T = Constant, where the value of the
constant depends on the amount of gas present and t is the absolute (or
Kelvin) temperature.
Ideal Gas Law
The Ideal Gas Law can be written in a slightly different manner from the
Generalized Gas Law: PV/T = nR, or PV = nRT. When written this way,
it is called the Ideal-Gas Law. R is the gas constant, and n is the number of
moles of gas. The gas constant can be examined experimentally as R =
0.082 liter atm/Kelvin moles. Knowing R, the fourth variable can be
evaluated if any three are known.
The gas Laws are valid for most gases at moderate temperatures and
pressures. At low temperatures and high pressures, gases deviate from the
above Laws because the molecules are moving slowly at low temperatures
and they are closer together on the average at higher pressures.
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