States States 1 States Three states of matter : solid, liquid and gas Next Slide States Three states of matter : solid, liquid and gas Melting : change from solid to liquid Boiling : change from liquid to gas Solidifying : change from liquid to solid Condensing : change from gas to liquid

Latent heat of fusion States 2 States Next Slide Latent heat of fusion Certain amount of energy is absorbed when a substance changes from solid to liquid without a change of temperature. The same amount of energy is released when the substance changes from liquid to solid without a change of temperature. This amount of energy is called the latent heat of fusion.

Latent heat of vaporization States States 3 Next Slide Latent heat of vaporization Certain amount of energy is absorbed when a substance changes from liquid to gas without a change of temperature. The same amount of energy is released, when the substance changes from gas to liquid without a change of temperature. This amount of energy is called the latent heat of vaporization.

Internal energy and States Next Slide Internal energy and States Internal energy : sum of K.E. and P.E. of all particles K.E. : the energy of vibrations of the particles P.E. : intermolecular forces among the molecules K.E, P.E. and states Diagram Specific latent heat of substances : the amount of energy required to change the state of a substance with a mass 1 kg without a change in temperature

Experiment States 5 States Next Slide Experiment Experiment to find the specific latent heat of fusion of ice Diagram Experiment to investigate the change of state Diagram Heating curves and cooling curves Diagram Example Diagram

Evaporation and applications States States 6 Next Slide Evaporation and applications Evaporation : Liquid changes to gas at a temperature below the boiling point Differences between evaporation and boiling Diagram Examples of latent heat Photo

END of Change of State

Back to States 4 States Click Back to gas gain in K.E. liquid solid gain in K.E. gain in P.E.: latent heat of vaporization heat of fusion

States 5 States Next Slide We use the following set-up to investigate the specific latent heat of vaporization. control apparatus experimental Joulemeter (or kilo-watt hour meter) water melted by the heat from the surroundings by the heat from the surroundings + heater

Back to States 5 States Click Back to Mass of experimental cup + water = 0.045 kg Mass of control cup + water = 0.014 kg Mass of water melted by heater only = (0.045  0.014) kg = 0.031 kg Initial Joulemeter reading = 15600 J Final Joulemeter reading = 29800 J Energy supplied = (29800  15600) J = 14200 J Specific latent heat of fusion of ice = (14200  0.031) J/kg = 458000 J/kg

States 5 States Next Slide Some wax is placed in a test-tube with a thermometer. The test-tube is heated until the wax melts and becomes liquid and then the test-tube is left alone. The temperature vs time graph is plotted according to the data recorded. We find that the central part of the curve levels off. During that duration, the liquid changes back to solid, i.e. a change of state.

Back to States 5 States Click Back to Experimental setup and the graph: temperature solid solid-liquid liquid melting point time wax in liquid form thermometer

States 5 States Next Slide Heating curve : temperature gas boiling solid solid-liquid liquid liquid-gas gas boiling point melting time temperature

Back to States 5 States Click Back to Cooling curve : temperature gas solid solid-liquid liquid liquid-gas gas boiling point melting temperature time

States 5 States Next Slide What is the energy required to change a 2 kg block of ice at 0C to steam at 100C? (specific heat capacity of water : 4200 J/(Ckg) specific latent heat of fusion : 336000 J/kg specific latent heat of vaporization : 2280000 J/kg)

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Back to States 6 States Click Back to Evaporation Boiling Occurs at any temperature Occurs at a definite temperature: the boiling point Occurs at the surface Occurs within the liquid No bubbles Bubbles appear

States 6 States Next Slide Sweating : evaporation of sweat carries heat away from the body

States 6 States Next Slide Refrigerator : Freon evaporates inside a refrigerator and carries away some heat. At the back of the refrigerator, freon vapour condenses and releases the heat.

Back to States 6 States Click Back to You feel cold when you are out of a swimming pool in winter, though it is warm when you are in the swimming pool.