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Back Chemical Chemical Engineering Dictionary Thermodynamics Property of a System - Types of Properties, Intensive & Extensive Properties Determination

Property of a System - Types of Properties, Intensive & Extensive Properties Determination

Definition:

Property is defined as the characteristic of any system. Some known properties are pressure (P), Temperature (T) , Volume (V) and mass(M). Some properties of system which are less familiar are Viscosity, Modulus of elasticity, thermal conductivity, electric resistivity, thermal expansion coefficient

Some properties of the system are independent and some properties are dependent on other property like density is defined as the ratio of mass per unit volume (since mass and volume are properties)

?=m/v

Generally, density depends upon temperature and pressure. In the case of gases density is directly proportional to pressure, as pressure increases or decreases density increases or decreases. Density is inversely proportional to temperature. As temperature are increased density decreases. And as temperature is a decreased density increase.

Density of liquid and solid remain constant. Since liquid and solid are incompressible substances. Pressure has almost negligible impact on the density of liquids and solids. However temperature does impact the density of solids and liquids.

Specific gravity or relative density is defined as the density of substance relative to the density of well known substance. It is the ratio of density of substance to the density of specified substance at a standard pressure ( water is taken usually at 4oc density of water=1000kg/m3)

Formula

?s =?/?H2O

Since specific gravity is a ratio, so it has no unit. The substance with specific gravities higher than 1 is heavier than water therefore they will not float on water. Only substance with the specific gravity less than 1 will float on water.

One of the most common properties in thermodynamics is called specific volume. Specific volume is inverse of the density.i.e defined as volume per unit mass.

Types of properties

There are two types of properties

  1. Intensive properties
  2. Extensive properties

INTENSIVE PROPERTIES

It is the property of a system which is dependent on the size of a system such as temperature, pressure and density.

EXTENSIVE PROPERTIES

It is the property of the system which is dependent on the size as well as the extent of the system. Such as mass M.

DETERMINATION OF INTENSIVE AND EXTENSIVE PROPERTY

In order to find out whether the property of the system is intensive or extensive bisect the system In to two equal portion. In each portion intensive properties will have the same value while extensive properties will have half values as shown in the figure below.

Generally the e intensive properties are denoted by lowercase letters (mass m) and extensive properties are denoted by uppercase letters (pressure P and temperature T)

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