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| Effect of Temperature and Pressure on States of Matter |
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| When we heat a solid, we add energy to the system increasing the vibration of the particles. Eventually these particles break free from their binding forces and melt. The normal melting point of a crystal is the temperature at which it melts under one atmospheric pressure. Increase in pressures usually raises the melting point. |
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| When the liquid produced by melting a crystal is cooled, it eventually solidifies or freezes. The temperature at which the liquid freezes under one atmospheric pressure is the normal freezing point. |
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| Most solids when heated eventually melt but few undergo sublimation. In this phase change, the solid goes directly into a gaseous phase and bypasses a liquid phase. |
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| For example: iodine and camphor |
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| Sublimation depicted at submicroscopic level |
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| On heating a liquid, the energy of the particles increase. They overcome the inter-particle force of attraction and turn into a gas or vapor at its boiling point. Boiling point of the liquid is a temperature at which the vapor pressure of the liquid is equal to the atmospheric pressure. Changing the atmospheric pressure can change boiling point of a liquid. |
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| For instance water boils on a mountain top at a much lower temperature than at sea level. Atmospheric pressure being less requires lesser thermal energy to get vapor pressure equal to atmospheric pressure. |
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| Effect of pressure on air and liquids |
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| A 100 mL syringe whose nozzle is plunged/closed by inserting a rubber cork is taken. 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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