To understand the difference between a pure substance and a mixture, let us understand the difference between a physical and a chemical change. In the previous chapter, we have learnt about a few physical properties of matter. The properties that can be observed and specified like colour, hardness, rigidity, fluidity, density, melting point, boiling point etc. are the physical properites.
The interconversion of states is a physical change because these changes occur without a change in composition and no change in the chemical nature of the substance. Although ice, water and water vapour all look different and display different physical properties, they are chemically the same.
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Which of the following are chemical changes ?
- decaying of wood
- burning of wood
- sawing of wood
- hammering of nail into wood
Which of the following are physical changes ?
- melting of iron metal
- rusting of iron metal
- bending of an iron rod
- drawing a wire of iron metal
Which of the following are physical changes and which are chemical changes ?
Glowing of an electric bulb