CHAP. 1: BASIC TERMS [CONTENTS] 25
1.1.2 Closed system
A chemical system exchanging energy but not matter with its surroundings is aclosed system.
1.1.3 Open system
A chemical system exchanging both energy and matter with its surroundings is anopen sys-
tem.
Example
Differences between individual types of chemical systems may be demonstrated using the example
of making coffee. The pot on the heater represents a (practically) closed system until the water
is brought to the boil. At the boiling point, when steam is leaking from the pot, it becomes an
open system. The ready-made coffee kept in a thermos bottle represents a simple model of an
isolated system.1.1.4 Phase, homogeneous and heterogeneous systems
The termphaseis used for that portion of the investigated system volume in which its proper-
ties are constant or continuously changing in space. If a system behaves in this way throughout
all its volume, we call it ahomogeneous system. If a system contains more phases, we call
it aheterogeneous system.
Example
Let us imagine a bottle of whisky. How many phases does this system consist of?