A1.(a) Melting point: The constant temperature at which a solid changes into liquid state by abso... more A1.(a) Melting point: The constant temperature at which a solid changes into liquid state by absorbing heat energy is called melting point. (b) Boiling point: It is the temperature at which a liquid changes into vapour under atmospheric pressure. (c) Evaporation: The slow passing of molecules of a liquid into gaseous state at a temperature below its boiling point. (d) Freezing: It is a process in which a liquid changes into solid state by giving out heat energy. a2.Boiling point of a liquid can be raised by increasing the atmospheric pressure. A3.On heating, solid wax melts into liquid wax, which on further heating, is converted into wax vapours. These changes can be seen in a burning candle. The candle is made up of a solid wax. When we light a candle, the wax near its wick melts. The molten wax rises up the wick and is converted into wax vapour. The wax vapour mixes with oxygen in the air and burns. In a lighted candle, you can see the solid and the liquid states of wax. The vapour of wax can be seen rising from the wick for some time after the candle is put out.
A1.(a) Melting point: The constant temperature at which a solid changes into liquid state by abso... more A1.(a) Melting point: The constant temperature at which a solid changes into liquid state by absorbing heat energy is called melting point. (b) Boiling point: It is the temperature at which a liquid changes into vapour under atmospheric pressure. (c) Evaporation: The slow passing of molecules of a liquid into gaseous state at a temperature below its boiling point. (d) Freezing: It is a process in which a liquid changes into solid state by giving out heat energy. a2.Boiling point of a liquid can be raised by increasing the atmospheric pressure. A3.On heating, solid wax melts into liquid wax, which on further heating, is converted into wax vapours. These changes can be seen in a burning candle. The candle is made up of a solid wax. When we light a candle, the wax near its wick melts. The molten wax rises up the wick and is converted into wax vapour. The wax vapour mixes with oxygen in the air and burns. In a lighted candle, you can see the solid and the liquid states of wax. The vapour of wax can be seen rising from the wick for some time after the candle is put out.
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