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| Effect of Pressure on Matter
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| Pressure has little effect on the state of solids and liquids as the inter-particle distance is already minimized in these situations. However, the effect of pressure in case of gases is considerable.
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| Condensation
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| The change of state from the gaseous form to the liquid form is called condensation. It is also called liquefaction. A good example of this process is that of water vapour in atmosphere condensing to form rain.
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| By applying pressure to a gas the particles come closer and start condensing to the liquid state. By applying pressure and reducing temperature one can liquefy gases. A good example is the liquefaction of petrol gas from oil refineries into LPG cylinders (liquefied petroleum gas).
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| Experiment
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| A 100 mL syringe is taken whose nozzle is plugged or closed by inserting a rubber cork. The plunger is drawn out such that the whole space is occupied by air. When the plunger is pushed back into the syringe we notice that the air inside the syringe decreases i.e., it is compressed.
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| The experiment is repeated with water replacing the air in the syringe. It is found that the plunger cannot be pushed into the syringe. This is because liquids are hardly compressible. This shows that pressure does not produce much effect upon liquids.
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| Accordingly, temperature and pressure determine the state of a substance either solid, liquid or gas.
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