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22nd Mar 2019 @ 12 min read
All Substances behave differently based on their characteristics and attributes. These characteristics and attributes are the properties of matter. With the knowledge of properties of substances, chemists can predict their behaviour, nature, and their interactions with other substances. Some of these properties can merely be identified by simple observation while some require experimentation.
There are two ways in which we can classify properties of matter. Based on how properties are determined, they can be classified into two categories: physical properties and chemical properties. Based on the dependence of properties on the amount of a substance, we can classify them into intensive properties and extensive properties. The figure below explains the same.
Physical properties can be measured or determined without altering the chemical identity of a substance. The chemical composition of a substance remains fixed during the measurement of physical properties; in other words, there is no chemical change.
Note: In the estimation of physical properties, no chemical change occurs, but physical change may occur. Physical change is a change in which physical appearance is affected. There is no breaking or formation of chemical bonds. For example, Ice melts to water is a physical change, no chemical composition is altered. Some of the examples of physical change are melting of solids, boiling of liquids, freezing of liquids, physical mixing, separation of a mixture, shape deformation, ripping of paper.
Examples of physical properties are taste, colour, odour, density, melting point, boiling point etc.
Chemical properties can only be estimated through a chemical change. It means a substance changes its original identity during the measurement of its chemical properties. The chemical change is nothing but a chemical reaction. Substances whose properties are to be estimated are lost during the measurement. Chemical properties of a substance are indications of the chemical nature of the substance like reactivity towards acids and bases, combustibility, flammability, acidity, basicity.
Chemical change alters the chemical composition of a substance. The original substance is destroyed. Consider the corrosion of iron. In corrosion, iron reacts with oxygen to form iron oxide. The original iron is permanently destroyed to produce iron oxide. The chemical composition of the original material is completely altered. Other examples of chemical change are milk turning sour, burning of paper, combustion of petrol or any other fuel, fermentation.
A property of a substance or system is called intensive when it is independent of the amount of the substance. It is a bulk property. The property does not change with the size of a system. Intensive properties are the same for 1 gram of a substance or 1 kilogram, 1 cm3 or 1 m3. The density of water is 1000 kg m−3, and it is an intensive property. So, the density of water always will be 1000 kg m−3 irrespective of the mass and/or volume of water.
Some of the examples of intensive properties are density, colour, temperature, conductivity, refractive index, malleability, lustre, hardness etc.
Extensive properties are which depend on the amount of a substance or the size of a system. An extensive property is directly proportional to the amount of a substance. One litre of a bottle holds one-litre water and two litres of a bottle holds two-litre water. Thus, the volume is an extensive property. An extensive property is the additive of subsystems. In other words, the extensive property of the total system is the sum of extensive properties of every subsystem. If there are two water bottles of the volume of 1 L each, the total volume is the sum of each bottle which is 27 L.
Examples of extensive properties are mass, volume, length, enthalpy, internal energy, entropy etc.
Note: The ratio of two extensive properties is always an intensive property. For example, the ratio of mass and volume is density; mass and volume are extensive properties while density an intensive property.
The table below lists various properties.
|Gibb free energy||Physical||Extensive|
|Molar Gibb free energy||Physical||Intensive|
|Specific heat capacity||Physical||Intensive|
|Heat of combustion||Chemical||Intensive|
|Heat of formation||Chemical||Intensive|
|Thermal expansion coefficient||Physical||Intensive|
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