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Definitions

Definitions. energy -. the capacity to do work or produce heat. kinetic energy - energy of motion potential energy - energy of position. Exothermic. When heat ( q) flows away from object or reaction. Endothermic. When heat ( q) flows into an object or a reaction. Heat Transfer.

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Definitions

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  1. Definitions energy- the capacity to do work or produce heat kinetic energy - energy of motion potential energy - energy of position Exothermic When heat (q) flows away from object or reaction Endothermic When heat (q) flows into an object or a reaction

  2. Heat Transfer between two objects at different temperatures Sensible heat - heat associated with a temperature change Specific heat capacity - the amount of energy needed to change the temperature of 1 g of substance by 1 oC (or K) Thermal Equilibrium - when objects reach a constant temperature substance specific heat J/g.K Al ---------------------- 0.902 Cu ---------------------- 0.385 Fe ---------------------- 0.451 NH3(l) ----------------- 4.70 CCl4(l) ----------------- 0.861 H2O(l) ----------------- 4.18 H2O(s) ----------------- 2.06 CCl2F2(g) ------------- 0.598

  3. Example Problem heat transferred = (S.H.)(mass)(DT) Example: A lake that is 1 square mile and 10 feet deep contains 7.9 x 109 L of water. How many joules of energy must be transferred to the lake to raise the temperature by 1 oC? (densityH2O = 1.0g/mL) Mass of water = 1000 mL 1.0 g 7.9 x 109 L x x = 7.9 x 1012 g mL 1.0 L 4.184 J Heat transferred = x 7.9 x 1012 g x (+1 oC) g.oC = 3.3 x 1013 J

  4. Heat Transfer Between Substances What is the final temperature of 323.4 g H2O initially at 21.7 oC, when 79.2 g of iron 71.9 oC are added? Specific Heat Capacity J/g.oC H2O 4.184 Fe 0.449 The fundamental principle here is that the energy lost by the substance initially at higher temperature is equal to the energy gained by the substance initially at lower temperature. -qhotobject = qcold object - qFe = qH2O -(S.H.Fe)(m)(Tf - Ti,Fe) = (S.H.H2O)(m)(Tf - Ti,H2O) -(0.449 J/g.oC)(79.2 g)(Tf - 71.9 oC) = (4.184 J/g.oC)(323.4 g)(Tf - 21.7 oC) Tf = 23.0 oC

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