The spreading out and mixing of a substance with another substance due to motion of its particles is called diffusion It is based on motion of its particles and is fastest in gases and slowest in solids. The rate of diffusion increases on increasing temp. (kinetic energy increases giving faster motion to particles). Light gases diffuses faster than heavier ones. Egs- smell of food reaches us even at considerable distances, smell of perfume is spread all over the room, spreading of ink in water on its own when put undisturbed for sometime, dissolving of oxgen and co2 in water for survival of aquatic plants and animals, disappearance of chalk from blackboard when leave uncleaned for 15 days.
The common unit of measuring temperature is degree celsius and the SI unit of measuring temperature is Kelvin
0 degree = 273 kelvin / kelvin scale temp. = celsius scale temp. + 273
melting point of ice = 0 degree /273k and boiling point of water is 100 degrees/ 373k.
Change of state from one form to other can be done by- 1.Changing the temperature 2.Changing the pressure. Effect of change in temperature : The process of changing solid to liquid by heating is called melting/ fusion. The temp. at which this happen at atmospheric pressure is called melting point of that substance. This happens due to weakening of attraction forces due to high kinetic energy in particles.
The process in which a liquid substances changes into gas rapidly on heating is called boiling. The temp. at which this takes place at atm pressure is called its boiling point. The process of changing a gas to a liquid by cooling is called condensation. This happens as gas looses its kinetic energy and particles come closer. When liquid changes to solid by cooling it is called freezing.
LATENT HEAT OF FUSION: The latent heat of fusion of a solid is quantity of heat in joules required to convert 1kg of solid to liquid without any change in temperature. It is 3.34*10^5 joules per kg. Heat energy is used up in changing the state by overcoming the force of attraction between the particles so the temp. remain the same even after supply of energy, further heating increases the kinetic energy rising temp. Ice at o degree is more effective in cooling than water at same temp. as for melting each kg of ice takes latent heat from substance whereas water do not have any such latent heat. When solid melts it absorbs heat from liquid also when liquid freeze to form a solid an equal amount of heat is given out.
Latent heat of vaporization: It is the quantity of heat in joules required to convert 1 kg of liquid to vapors/gas without change in temp. The temp. don’t rises due to overcoming force of attraction. When water changes to steam it absorbs latent heat, when steam condenses to form water an equal amount of latent heat is given out therefore burns caused by steam is much severe than boiling water as steam contains more heat than water.
Sublimation- the changing of solid directly into vapors on heating and gas on solid by cooling; substances = ammonium chloride, iodine, camphor, naphthalene ,etc. solid co2(dry ice) sublimes to form liquid co2.
Effect of change of pressure- Gases can be liquefied by applying pressure and lowering temp. Dry ice is extremely cold substance it is used as deep freeze to keep food and ice cream cold. Solid co2 changes to Gas by decrease in pressure and higher atmospheric temp. So it is always kept under high pressure.
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