Thermchemistry_I_Review_and_Enrichment (1)

Thermchemistry_I_Review_and_Enrichment (1) - REVIEW AND...

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REVIEW AND AMPLIFICATION OF THERMOCHEMISTRY AND THERMODYNAMICS The change in x = x = x f - x i Energy? The capacity to do work or to transfer heat. Kinds of energy? Kinetic energy ½mv 2 Change in gravitational potential energy mg h H rxn Change in chemical potential energy (at constant pressure) E rxn (at constant volume) Change in internal energy E = C V T (always true) Radiant energy E photon = hf Change in nuclear energy E = mc 2
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FIRST LAW OF THERMODYNAMICS Conservation of Energy Examples: KE and P.E; Heat; Reaction—Exothermic, Endothermic Energy transferred to a system Sign convention: q is positive if heat is added to the system. w is positive if heat is added to the system. q heat work w Change in Internal Energy = E f -E i = E = q + w EXAMPLE 1: 6000 J of heat are added to a system. It does 5000 J of work on the surroundings. What is E ? E = 6000J – 5000J = 1000J
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PV Work (magnitude) Work = w = Fd =(F/A)(dA) =P V (sign convention) w = - P ext V () 3 52 0.1 1 1 1.013 10 / 1 101.3 or 11 1 m atm L x N m xx x a Nm J tm L = Units: (atm)(L) =
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EXAMPLE 2: 5000. J of heat are added to a gas. Its volume increases from 10.0 to 50.0 L by expanding against an external pressure of 1.00 atm. What is E ? q = 5000 J ( )( ) 1.0 50 10 1 atm L wP V =− ∆ =− 101.3 J x La tm 4050 J E = q + w = 5000 -4050 = 950J EXAMPLE 3: An ideal gas is compressed isothermally ( T = 0) from 80. to 20. L. The external pressure is 1.1 atm. What are E, q and w ? Why? E = 0 1.1 20 80 1 atm L V 101.3 J x 6700 J = E = 0 = q + w So q = -w w = 6.7 kJ q = -6.7 kJ
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Adiabatic (q = 0) processes: The heat capacity is the quantity of heat required to raise the T of a substance by 1 ºC. E = q + w = w E = C V T Qualitative examples of nearly adiabatic processes—when done quickly: Expansions: CO 2 cartridge; making snow (20 atm) Compressions: inflating tire; igniting paper (like diesel engine) Chang
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EXAMPLE 4: 1.00 mol CO 2 gas (C V = 28.5 J/(mol·K)), at 60. atm, and 30. ºC expands adiabatically against an external pressure of 1.0 atm.
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This note was uploaded on 11/02/2011 for the course CHEM 126 taught by Professor Biolsi during the Spring '08 term at NJIT.

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Thermchemistry_I_Review_and_Enrichment (1) - REVIEW AND...

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