CHAP. 2: STATE BEHAVIOUR [CONTENTS] 42
Chapter 2
State behaviour
The temperature, pressure, volume and amount of a pure substance are not independent. In
a homogeneous system, any three of these quantities may be chosen, with the fourth being
implicitly given. For instance, we may choose the amount of a given substance, the volume
in which it is enclosed, and its temperature. The pressure as the fourth quantity is then
implicitly given. The state behaviour of a substance (or, more accurately, the description of
its state behaviour) is expressed by the relation between its temperature, pressure, volume and
amount of substance. We obtain this relation either experimentally (i.e. we measure the state
behaviour) or theoretically (i.e. we calculate the state behaviour).
The state behaviour of a homogeneous mixture is expressed by the relation between the tem-
perature, pressure, volume and the amount of substance of its components. In ak-component
mixture, we may choose any (k+ 2) of the (k+ 3) quantities, with the (k + 3)rd quantity
being implicitly given. We may, e.g., choose the amount of a given mixture, its composition
(i.e.kâ 1 data), temperature and pressure. The volume is thus implicitly determined.