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Published byGervais Webster Modified over 9 years ago
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How are they related?
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Energy Encountered Daily
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Is Heat Used or Released? Endothermic reactions used heat from the surroundings Sweating Refrigeration Exothermic heat releases heat to the surroundings Hot hands Combustion Exercise
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Endothermic Reactions Decrease in kinetic energy decrease in temperature heat will transfer from the environment to the system resulting in a cooler environment Absorbs heat from its surrounding. The system gains heat Positive value for q H = q = 0 H products H reactants
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Exothermic Reactions Increase in kinetic energy increase in temperature of system heat released to the environment resulting in a hotter environment Releases heat to its surroundings The system loses heat Negative value for q H = q = 0 H products H reactants
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Enthalpy Heat content for systems at constant pressure Symbol is H Terms heat and enthalpy are used interchangeably for this course H = q = m C T Heat moves from ________ to ___________.
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Law of Conservation of Energy Energy is not lost or gained in a chemical reaction In a chemical reaction potential energy is transferred to kinetic energy
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Thermochemical Equations An equation that includes the heat change Example: write the thermochemical equation for this reaction CaO(s) + H 2 O(l) Ca(OH) 2 (s) H = -65.2 kJ CaO(s) + H 2 O(l) Ca(OH) 2 (s) + 65.2 kJ
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Stoichiometry and Thermochemistry Tin metal can be extracted from its oxide according to the following reaction: SnO 2 (s) + 4NO 2 (g) + 2H 2 O(l) + 192 kJ Sn(s) + 4HNO 3 (aq) How much energy will be required to extract 59.5 grams of tin?
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How to solve 1. Use your stoichiometry 2. Treat heat as a reactant or product SnO 2 (s) + 4NO 2 (g) + 2H 2 O(l) + 192 kJ Sn(s) + 4HNO 3 (aq) 59.5 g Sn 1 mol Sn 192 kJ 1 g Sn 1 mol Sn
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If an Object feels hot, it means it is undergoing a change with a H that is: a. positive b. negative c. whether the object feels hot or not is unrelated to its H d. I don’t know
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If the object feels hot, it means it is undergoing : a. an exothermic reaction b. an endothermic reaction c. whether it feels hot or not is unrelated to whether it is undergoing an exothermic or an endothermic change
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How does ice melt?
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Molar Heat of Fusion Heat absorbed by one mole of a substance during melting Constant temperature H fus H 2 O(s) H 2 O(l) H = 6.01 kJ/mol
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Molar Heat of Solidification Heat lost when 1 mole of a liquid solidifies Temperature is constant H solid H fus = - H solid H 2 O(l) H 2 O(s) H = -6.01 kJ/mol
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Molar Heat of Vaporization Heat needed to vaporize 1 mole of a liquid H vap H 2 O(l) H 2 O(g) H vap = 40.7 kJ/mol
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Molar Heat of Condensation Heat released when 1 mole of vapor condenses H cond H 2 O(g) H 2 O(s) H cond = -40.7 kJ/mol H vap = - H cond
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Phase Change Diagram for Water
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Phase Change Diagram
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The House that Heats Itself http://www.sciencefriday.com/videos/watch/ 10007 http://www.sciencefriday.com/videos/watch/ 10007
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Calorimetry Method used to determine the heat involved in a physical or chemical change. Relies on the law of conservation of energy
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Calorimeter
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Simple Calorimeter
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Calorimetry Math Heat gained by the water = q Heat lost by the system = -q mC T = q T = T f –T i, m = mass, C = specific heat q gained by water = q lost by system q water = - q system mC T = -mC T (mass H 2 O)(spec. heat H 2 O)( T H 2 O) = - (mass sys)(spec. heat sys)( T sys)
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