Systems, Properties and Processes

Key Concepts

• Systems
• Macroscopic Properties
• Thermodynamics Processes

Introduction:

In this session, we will be looking at various attributes of the particles of substances, such as various kinds of systems, properties and thermodynamic process, in detail. This is the basic knowledge one should possess in order to learn thermodynamics

Explanation:

Systems: 

The part of the universe which is considered for a study is called a system. The rest of the universe is called the surroundings. The system is separated from its surroundings by a boundary. 

Universe = system + surrounding 

Examples of systems: 

The pictures below show some examples of systems. Each of these systems comprises an uncountable number of particles subjected to a set of identical conditions. 

Types of systems: 

Open system: 

Hot coffee in the cup is a system where the heat energy flows out of the system, and also, the water in the form of steam escapes the system. A system is said to be open if it can exchange both matter and energy with its surrounding. Thus, a hot cup of coffee is an open system. 

Closed system: 

Hot water inside a copper bottle with the lip on is a system where the heat escapes to the surroundings through the conducting walls of the bottle. However, no water or steam escapes the bottle. A system is said to be closed if it can exchange energy with its surroundings but not matter. Thus, a bottle of hot water with the lid on is a closed system. 

Isolated system: 

Hot water inside a well-insulated thermos flask with the lip on is a system where neither heat nor steam escapes to the surroundings. Also, no heat or steam enters the system. A system is said to be isolated if it can exchange neither energy nor matter with its surrounding. Thus, a well-insulated thermos flask of hot water with the lid on is an isolated system. 

Macroscopic properties of a system: 

The properties of a system that are associated with the bulk or macroscopic state of a system are called the macroscopic properties of a system. 

For example, pressure, volume, temperature, density, internal energy, viscosity, transparency, refractive index, color, etc.  

Classification of macroscopic properties of a system: 

Thermodynamic Processes: 

A thermodynamic process is said to occur when a system changes its state (pressure, volume, temperature). 

For example, cooling down of a cup of hot coffee, melting of ice, freezing of water, etc. 

Isothermal process: 

When a process is carried out in such a way that the temperature of the system remains constant throughout, it is called an isothermal process. 

Change in temperature, ΔT = 0 

In such cases, the heat may flow into or out of the system to maintain the constant temperature. 

Adiabatic process: 

When a process is carried out in such a way that no heat flows into or out of the system, it is called an adiabatic process. 

Change in heat, ΔQ = 0 

In such cases, the system is completely isolated from the surrounding. 

Isochoric process: 

When a process is carried out in such a way that the volume of the system does not change, it is called an isochoric process. 

Change in heat, ΔV = 0 

In such cases, the pressure and temperature of the system may change. 

Isobaric process: 

When a process is carried out in such a way that the pressure of the system does not change, it is called an isobaric process. 

Change in heat, ΔP = 0 

In such cases, the volume and temperature of the system may change. 

Questions and answers: 

1. Write down the kind of process to which the following equations correspond to. 

1. ΔQ = 0 

2. ΔT = 0 

3. ΔP = 0 

4. ΔV = 0 

Answer: 

2. An open system allows the transfer of ——–, whereas a closed system allows the transfer of ——–. 

1. Heat, matter 

2. Heat and matter, heat 

3. Heat, heat, and matter 

4. Matter, heat 

Ans: 

b. Heat and matter, heat

Summary

• An entity consisting of a collection of particles experiencing the same set of conditions is called a system.
• The part of the Universe which is considered for a study is called a system. The rest of the universe is called the surroundings. Universe = system + surrounding.
• A system is said to be open if it can exchange both matterand enerpy with its surrounding.
• A system is said to be closed if it can exchange energy with its surrounding but not matter.
• A system is said to be isolated if it can exchange neither energy nor matter with its surrounding.
• The properties of a system which are associated with the bulk or macroscopic state of a system are called the macroscopic properties of a system. For example, pressure, volume, temperature, density, internal energy, viscosity, transparency, refractive index, color etc.
• Macroscopic properties of a system can be either extensive (depend upon the mass or size of the system) or intensive (depend upon the nature and independent of the mass or size of the system).
• A thermodynamic process is said to occur when a system changes its state (pressure, volume, temperature).