Matters in our surroundings

III. Change of State of Matter

​Matter can change from one state to another by changing temperature or pressure.

1.​ ​Effect of Temperature:
○​ ​Melting: Solid → Liquid (at Melting Point).
○​ ​Boiling: Liquid → Gas (at Boiling Point).
○​ ​Sublimation: Direct change from Solid → Gas without becoming liquid (e.g.,
Ammonium Chloride).
○​ ​Deposition: Direct change from Gas → Solid.
2.​ ​Latent Heat (The "Hidden" Heat):
○​ ​Latent Heat of Fusion: The heat energy required to change 1\text{ kg} of a
solid into a liquid at atmospheric pressure at its melting point.
○​ ​Latent Heat of Vaporization: The heat energy required to change 1\text{ kg}
of a liquid into a gas at atmospheric pressure at its boiling point.

​IV. Evaporation

​The phenomenon of change of a liquid into vapors at any temperature below its boiling point.

​Factors affecting the rate of Evaporation:

●​ ​ urface Area: \uparrow Area = \uparrow Evaporation (e.g., spreading clothes to dry).
S
●​ ​Temperature: \uparrow Temp = \uparrow Evaporation.
●​ ​Humidity: \uparrow Humidity = \downarrow Evaporation.
●​ ​Wind Speed: \uparrow Wind Speed = \uparrow Evaporation.
●​ ​Note: Evaporation always causes a cooling effect. This is why we wear cotton
clothes in summer and why water stays cool in earthen pots (Matka).​
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​V. Important Units​

○​ T​ emperature: SI unit is Kelvin (K).
○​ ​Formula: T(K) = T(°C) + 273.15
○​ ​Pressure: SI unit is Pascal (Pa).