We were discussing the basic of engineering thermodynamics in our previous post i.e. Thermodynamics system, boundary and surrounding, we have also seen the various classes of thermodynamics system there.

Today we will focus here the concept of thermodynamic equilibrium in this post and also we will see here the properties of the system.

Thermodynamic system will be considered in thermodynamic equilibrium, if system is meeting the condition of the three important types of equilibrium as mentioned below.
1. Mechanical Equilibrium
2. Thermal Equilibrium
3. Chemical equilibrium

### Mechanical Equilibrium

A system will be considered in the state of mechanical equilibrium if there is no unbalanced force within the system or between system and its surrounding. Pressure must be same at each point within the system and should not vary with respect to time.Â

If there is presence of unbalanced force within the system or between system and its surrounding, then system will not be considered in the state of mechanical equilibrium and in this situation only system or system and its surrounding will go through state change for securing the state of mechanical equilibrium.

### Thermal Equilibrium

In order to consider a system in the state of thermal equilibrium, temperature must be same at each point within the system and should not vary with respect to time. If system is not meeting this criterion, in that situation system will go through state change for securing the state of thermal equilibrium.

### Chemical equilibrium

In order to consider a system in the state of chemical equilibrium, if there is no chemical reaction taking place within the system and chemical composition of the system is not changing with respect to time.

Any thermodynamic system must meet the above equilibrium state to be considered as system in the state of thermodynamic equilibrium. A thermodynamic system will be considered in the state of non-equilibrium, if system is not meeting anyone above equilibrium state.

Now let us see the properties of a thermodynamic system

### Thermodynamics properties

There are basically two types of properties of thermodynamics system

### Intensive property

Any property that will not be dependent over the mass of the system will be termed as intensive property. Intensive property will exist at a point in space. Pressure, temperature and density will be the good example of intensive property.

### Extensive property

Any property that will be dependent over the mass of the system will be termed as extensive property. Volume will be the good example of extensive property.

There is another important type of intensive property i.e. specific property. Specific property will always comes in per unit mass such as specific volume. Specific volume indicates the volume per unit mass and its unit will be cubic meter/kg in SI system.

We will discuss another topic in thermodynamics in our next post.
Do you have any suggestions? Please write in comment box.

Reference
Engineering thermodynamics by R.K Rajput
Engineering thermodynamics by P.K Nag