Page 16 - Instant notes

A1
PERFECT GASES

Key Notes
A gas is a fluid which has no intrinsic shape, and which expands
indefinitely to fill any container in which it is held.

The physical properties of a perfect gas are completely described
by the amount of substance of which it is comprised, its
temperature, its pressure and the volume which it occupies. These
four parameters are not independent, and the relations between
them are expressed in the gas laws. The three historical gas
laws—Boyle’s law, Charles’ law and Avogadro’s principle—are
specific cases of the perfect gas equation of state, which is
usually quoted in the form pV=nRT, where R is the gas constant.
The pressure exerted by each component in a gaseous mixture is
known as the partial pressure, and is the pressure which that
component would exert were it alone in that volume. For a
perfect gas, the partial pressure, p x , for n x moles of each
component x is given by p x =n x RT/V.
Dalton’s law states that ‘the total pressure exerted by a mixture of
ideal gases in a volume is equal to the arithmetic sum of the
partial pressures’. The quantity n A /n total is known as the mole
fraction of component A, and denoted x A . It directly relates the
partial pressure, p A , of a component A, to the total pressure
through the expression p A =x A P total .
Related topics Molecular behavior in perfect gases (A2) Non-ideal gases (A3)

Gases

A gas is a fluid which has no resistance to change of shape, and will expand indefinitely
to fill any container in which it is held. The molecules or atoms which make up a gas
interact only weakly with one another. They move rapidly, and collide randomly and
chaotically with one another.
The physical properties of an ideal gas are completely described by four parameters
which, with their respective SI units are:

● the amount of substance of which it is comprised, n, in moles;
● the temperature of the gas, T, in Kelvin;
● the pressure of the gas, p, in Pascal;
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● the volume occupied by the gas, V, in m .