ch14 - Heat Chapter Outline GENERAL PHYSICS Heat as Energy...

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Unformatted text preview: Heat Chapter Outline GENERAL PHYSICS Heat as Energy Transfer PHY 302K Internal Energy Chapter 14: Heat Specific Heat Maxim Tsoi Latent Heat and Phase Change Calorimetry Physics Department, The University of Texas at Austin http://www.ph.utexas.edu/~tsoi 302K - Ch.14 302K - Ch.14 Specific Heat Heat and Internal Energy Energy vs transfer of energy Energy per unit mass to change temperature by 1oC • Internal Energy (U) energy associated with the microscopic components of a system (atoms, molecules) • If a quantity of energy Q is transferred to a substance of mass m, changing its temperature by T, the specific heat of that substance is defined by c Includes kinetic and potential energy associated with translational, rotational vibrational motion of particles; bonding energy • SI unit: J / kg oC Q m T • Heat (Q) transfer of energy between a system and its environment due to a temperature difference between them Higher specific heat of water than that of sand is responsible for the pattern of airflow at a beach Mechanical equivalent of heat calorie (cal) energy necessary to raise the temperature of 1 g of water from 14.5o to 15.5oC (Calorie = kilocalorie) 1 cal = 4.186 J 302K - Ch.14 Example 1 302K - Ch.14 Latent Heat and Phase Change Calorimetry Latent heat of fusion and vaporization Measuring specific heat Energy transfer between substance and its environment • For an isolated system the sum of all the gains and losses of thermal energy must add up to zero! Change in temperature Qk 0 Phase change Energy needed to change the phase of a given substance: Q mL Technique for measuring the specific heat of a solid or liquid: raise the temperature of the substance to some value place it into a vessel containing cold water of known mass and temperature measure the temperature of the combination after equilibrium is reached Latent heat of fusion Lf melting or freezing Latent heat of vaporization Lv boiling or condensing 302K - Ch.14 Example 2 302K - Ch.14 1 Latent Heat and Phase Change SUMMARY From ice to steam If 100 W of power is supplied to a container (held at constant pressure) holding a 1-g cube of ice at -30oC, how long will it take to turn for the ice to steam at 120oC? Heat • Specific heat c Q m T • For an isolated system the sum of all the gains and losses of thermal energy must add up to zero Q k 0 • Energy needed to change the phase of a given substance Q mL cice= 2090 J/kg oC; Lf, ice= 333000 J/kg; cwater= 4186 J/kg oC; Lv, water= 2260000 J/kg; csteam= 2010 J/kg oC 302K - Ch.14 302K - Ch.14 2 ...
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