Page 17 - Bruno Linder Elementary Physical Chemistry

August 18, 2010 11:35 9in x 6in b985-ch01 Elementary Physical Chemistry

2 Elementary Physical Chemistry

of a substance are specified, the state of the system is said to be
specified. Actually, there is no need to specify all properties, because, as
a rule, the properties are interdependent. For example, if you know the
pressure, the volume and the number of moles n of an ideal gas, you can
figure out the temperature from the equation of state: [PV = nRT ].

1.2. Description of Some States of Matter
• Volume, V : a measure of occupied space.
• Pressure: force per unit area.
∗
• Temperature: hard to define rigorously, but in simple language it is a
measure of the degree of hotness or coolness for which all of us have an
intuitive feeling.
• Amount of substance: a measure of the amount of matter.

∗
Comment: When two objects (bodies) are brought in contact with
each other, the hotter body will cool, the colder body will heat up.
This is interpreted that heat (aform of energy) is flowing from the
hotter body to the colder one. This process will continue until no
more heat is transferred. When that happens the two bodies are
said to be in thermal equilibrium — and the temperatures of the two
bodies will be the same.

1.3. Units
The recommended units are SI (Systeme Internationale) units:

Length l meter, m
Mass m kilogram, kg
Time t second, s
Electric current I ampere, A
Temperature T Kelvin, K
Amount n mole, mol
All other physical quantities that we use can be derived from these. For
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example, volume is length cube or m . Some derived quantities have special
names. For example,

• Force in SI units is kg m s −2 or Newton, N.
s
• Pressure in SI units is kg m −1 −2 or pascal, Pa.
2
• Energy in SI units is kg m s −2 or joule, J.