I.2 Description of thermodynamic systems

I.2.1 State of matter

There are three states of matter: solid, liquid and gas. and we can switch from one state to another (Figure I.1).

 

 Figure I.1: Different changes in the physical state of matter

I.2.2 System classification

There are two types of system classification:

I.2.2.1 From the point of view of the matter contained in the system. There are two types of system:

1. Homogeneous system

A system is homogeneous if it consists of a single phase whose physical properties are the same throughout the matter.

Example

O₂, gas, H₂O liquid, ...etc.

2. Heterogeneous system

A system is heterogeneous if it comprises several phases, or if the single phase has different properties in different regions.

Example

water-ice, water-oil...etc.

I.2.2.2 Exchanges between system and external environment

The evolution of a system's state over time is determined by knowledge of the nature of exchanges with the outside world. These exchanges are of an energetic nature, such as work or heat. We distinguish three types of thermodynamic system:

1 Open system

The open system exchanges matter and energy with the external environment (Figure I.2)

                                                     Figure I.2: Open system

Example

Tree: exchange of CO₂ and O₂ mineral salts                                                        Heating           

                                 

2 Closed system

The closed system retains its quantity of matter, but exchanges energy with the external environment (Figure I.3).

 

                                           Figure I.3: Closed system

Example

Oil-bath heating.

  

3 Isolated system

An isolated system cannot exchange either matter or heat with the external

environment (Figure I.4)

Figure I.4: Isolated system

 

Example