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Ch9 - Thermodynamics Will the rxn happen The study of...

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Thermodynamics Kinetics The study of energy & its transformations Energy content of reactants & products Enthalpy Heat content Entropy Disorder Will the rxn happen? Section 9.0 How fast & by what mechanism will the reaction occur?
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H 2 + 1/2 O 2 barb2right H 2 O Ε nergy released = -237 kJ Thermodynamics predicts that the reaction is favorable. (negative E) However, no reaction is observed when H 2 and O 2 are mixed. THERMODYNAMICS
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Once a small amount of energy is added (spark) the reaction proceeds! KINETICS
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Section 9.1 Energy is neither created nor destroyed in any process. The “form” of the energy can change in a process. Heat: disorganized energy something we feel Work: organized energy something we see
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E system = q + w Heat: disorganized E Work: organized E E univ = E system + E sur = ZERO q > 0: heat is absorbed by the system q < 0: heat is released from the system Section 9.1 w > 0: work is done on the system w < 0: work is done by the system
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E system = - E sur E univ = E system + E sur = ZERO When the system absorbs E, the surroundings must release E. When the system releases E, the surroundings must absorb E. Section 9.1
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When the system absorbs E, the surroundings must release E. system Section 9.1 Solid Gas E in System Energy CO 2 (s) CO 2 (g)
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When the system absorbs E, the surroundings must release E. surroundings Section 9.1 Surroundings Energy E out Liquid Gas CO 2 (s) CO 2 (g) H 2 O (g) H 2 O (l)
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When the system absorbs E, the surroundings must release E. surroundings Section 9.1 Potential Energy CO 2 H 2 O (g) E out Liquid Gas Solid Gas E in system CO 2 (g)
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When the system absorbs E, the surroundings must release E. Section 9.1 Potential Energy Solid Gas E in CO 2 E out Liquid Gas H 2 O E univ = E system + E sur E univ = ZERO An appropriate number of molecules of H 2 O are condensing, compared to the molecules of CO 2 that are subliming, Such that E univ = ZERO
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E system written as E in text Section 9.1 Chemical rxn or phase transformation under study
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A system has 200 J of work done on it And releases 125 J of heat. What is E system ? E system = q + w E system = What is E sur ? E sur = - E system = What is E univ ? ALWAYS, ALWAYS ZERO Section 9.1
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E system = q + w Heat transferred: disorganized E E univ = E system + E sur = 0 Section 9.2 E = q = H Work: organized E Constant P Enthalpy
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Endothermic process: a process in which heat is absorbed into the system. H system = - H sur E univ = E system + E sur = 0 Exothermic process: a process in which heat is released from the system. Section 9.2 E = q = H @ constant P When the system is undergoing an exothermic process, the surroundings must be undergoing an endothermic process.
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Endothermic (from the system’s perspective) surroundings i H > 0 H = H prod - H react We (as part of the surroundings) perceive endothermic processes as feeling ____. We gave it our heat.
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