States of Matter
, Chapter 10, pp. 398-441.
(Ch 10) 7, 38, 40, 48, 52, 60, 77, 85, 92, 94, 103
All matter exists in one of three states of aggregation, i.e., gaseous
, or solid
, under most
conditions of temperature and pressure.
We are most familiar with normal conditions
(298 K = 25
and 1 atm pressure).
At this temperature and pressure, only a few substances are gases (for example):
HF, HCl, HBr, HI, CO, NO
He, Ne, Ar, Kr, Xe, Rn
Under normal conditions, gases
are generally “small” molecular species with nonmetallic elements
(low molecular weights).
The atoms within a gas molecule are held together by chemical bonds
(energies on the order of 10
kJ/mol); gas molecules are
not held together
All gases have the following characteristics:
Gases assume the volume and shape of the container;
Gases are the most compressible of the states of matter;
Gases mix evenly and completely;
Gases have much lower densities (larger volumes) than solids and liquids.
(1) State Variables
of gases is closely linked to their
the volume occupied by a gas far exceeds the total volume of all gas molecules, and this is coupled
with the notion that the intermolecular forces between molecules in a gas are very weak.
Here are the
four important macroscopic variables and a statement regarding their microscopic interpretation:
No. of Moles
Number of gas molecules;
Distances between gas molecules far exceeds distances within
Average kinetic energy of the gas molecules (speeds).
(atm, mm Hg, Pascals):
Strength and frequency of collisions between gas molecules and
walls of the container (measured as momentum transfer,
momentum = mass