Advanced Knowledge of Change of State

Physics

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Sublimation

Sublimation is the transition of a substance directly from the solid to the gas phase without passing through the intermediate liquid phase.

definition

Sublimation

Sublimation is the transition of a substance directly from the solid to the gas phase without passing through the intermediate liquid phase.
Examples is ammonium chloride when heated changes from solid to gas.Even camphor and dry ice undergo sublimation.

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Boiling point and normal boiling point

The boiling point of a substance is the temperature at which the vapour pressure of the liquid equals the pressure surrounding the liquid and the liquid changes into a vapour at STP.The normal boiling point (also called the atmospheric boiling point or the atmospheric pressure boiling point) of a liquid is the special case in which the vapour pressure of the liquid equals the defined atmospheric pressure at sea level, 1 atmosphere.

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Factors affecting boiling point

  • Pressure: If the external pressure is higher than one atmosphere, the liquid will boil at a higher temperature than the normal boiling point.
  • Molecule Types: Types of molecules in the liquid affect the boiling point of the liquid. If the force of attraction between the molecules is relatively strong, the boiling point will be relatively high. If the force of attraction between molecules is relatively weak, the boiling point will be relatively low.

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Boiling point and melting point of different substances

The boiling point is the temperature at which a material changes from a liquid to a gas (boils). 
Here are  boiling point of different substances:
pentane , Bromine , Water etc.
The melting point of a solid is the temperature at which it changes state from solid to liquid at atmospheric pressure.
Here are melting  point of different substances:
mercury , water Aluminum etc.

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Experimentally define melting point of ice

Here is the procedure to determine the melting point of ice:
1. Take some ice cubes and dry them using a filter paper and quickly put them in a beaker.
2. Place the beaker over a wire gauze kept over a tripod stand.
3. Suspend a thermometer (temperature range -10 to 110C) with the help of a clamp stand so that its bulb remains in the middle of the ice cubes.
4. Ice cubes are moderately heated by a gas burner and stirred continuously using a glass rod.
5. Note the temperature when the ice starts melting.Continue heating the ice.
6. Note the temperature when the ice has melted completely.
7. Record your observations in tabular form in one column and in another column.Now find the average of and which will give you the melting point of ice.

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Experimentally define boiling point of water

Here is the procedure for finding the boiling point of water :
1. Take about of distilled water in a boiling tube and add small pieces of pumice stone.
2. Close the mouth of the boiling tube with a rubber cork that has two bores and clamp it with the stand.
3. Introduce a thermometer (temperature range ) in one bore of the cork of the boiling tube. Keep the bulb of the thermometer  about above the surface of the water.
4. Then introduce one end of a delivery tube in the second bore of the cork.Place a beaker below the second end of the delivery tube to collect the condensed water.
5. Heat the boiling tube gently, preferably by rotating the flame.
6. Note the temperature when the water starts boiling.
7. Continue to heat the water till the temperature becomes constant, and the water remains boiling. Note the constant temperature .
8. Record your observations in tabular form  in one column and in another column.Now find the average of and which will give you the boiling point of water.
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