chapter11.4_slides

# chapter11.4_slides - 11/10/2009 Calorimetry: Science of...

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11/10/2009 1 Calorimetry: Science of measuring heat in physical or chemical processes. Calorimeter: A device used in calorimetry to measure the heat (i.e., energy transferred from one substance to another susbtance) Calorimeter is often used to measure the specific heat of an unknown substance. Insulation ensures that no energy is transferred in or out of the inner vessel. Suppose a hot object is placed in a cool water inside the inner vessel of a calorimeter The hot object will lose energy while the water will gain energy. However, the total energy of the system will remain the same. Therefore, Q cold : energy gain of the cold water, positive Q hot : energy loss of the hot object negative 0 hot cold Q Q hot cold Q Q or

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11/10/2009 2 A 125 g block of unknown substance with a temperature of 90 o C is placed in an insulated cup containing 0.326 kg of water at 20 o C. After reaching equilibrium, the system has a temperature of 22.4 o C. What is the specific heat of the unknown substance? Solution: The water gain thermal energy The unknown substance losses energy Solve for c x . hot cold Q Q ) ( , w i f w w cold T T c m Q ) ( , x i f x x hot T T c m Q hot cold Q Q ) ( ) ( , , x i f x x w i f w w T T c m T T c m C 90 C 20 C 4 . 22 C) J/(kg 4190 o , o , o o x i w i f w T T T c Water cycle
11/10/2009 3 A phase change occurs when the physical characteristics of the substance change from one form to another Common phases changes are Solid to liquid melting (e.g., ice to water) Liquid to solid freezing (e.g., water to ice) Liquid to gas boiling (e.g., water to vapor) Gas to liquid condensation Solid to gas Gas to solid temperature Phases changes involve a change in the internal energy, but no change in temperature - think about ice in water. Ice keeps melting, the ice/water

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## This note was uploaded on 01/02/2010 for the course PHY 101 taught by Professor Pralle during the Spring '08 term at SUNY Buffalo.

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chapter11.4_slides - 11/10/2009 Calorimetry: Science of...

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