Ma Physical Chemistry 9/14, 9/16, 9/18
Ma Physical Chemistry 9/14, 9/16, 9/18 CHEM 345
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This 3 page Class Notes was uploaded by Kayli Antos on Friday September 18, 2015. The Class Notes belongs to CHEM 345 at Towson University taught by Dr. Ma in Summer 2015. Since its upload, it has received 30 views. For similar materials see Physical Chemistry in Chemistry at Towson University.
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Date Created: 09/18/15
P Chem Ma Fall 2015 o The First Law Of Thermodynamics I Energy cannot be created nor destroyed only converted from one form to another I Work W il The amount of energy that can be transferred across the boundary between a suite IL system and its surroundings It can always be converted to raising or lowering a weight in the surroundings Work refers to any energy transfer that is not dependent on a temperature is not heat energy If work is done on the system work is positive If the system does work work is negative PressureVolume PV WorkEXpansion Work 9 o WZ x A Work is equal to the force a vector times the change in the boundary of the system a vector For an infinitesimal change in X it can be expressed as dw Fx d O O 99 99 Since FX and X are vectors in order to make them scaler the cosign of the angle between them must be added to the equation The force and change in X will be in opposite directions which adds cosl80O l to the equation to the right side Since Pex A eXternal pressure gtllt cross sectional area the equation can Pex A dx V Through more rearrangement the equation w fvz Pex dV is reached 1 be rewritten as dW O 9 Ideal Gas lsothermal EXpansion And Compression 3 Expamm Pr V T 9 Pg to T gt lrreversible Expansion The entire process can only go in one direction Occurs when P9X 0 and w 0 in a vacuum Or when PBX P2 and w ff 136de P2V2 V1 The work will be negative because the system is doing work on the surroundings gt Reversible Expansion When P9X P dP and w ff 196de 41mm this is the 1 1 maXimum amount of work a system can do for eXpansion The work will also be negative in this instance because the system is doing work 1 Compression gt Irreversible Compression PeX gt P gt Reversible Compression W ff Pede fv f PdV nRT 1n the minimum amount of work the surroundings can do on the system V2 gt V1 and w gt 0 Since w is positive the surroundings do work on the system gt Reversible Expansion Compression of ldeal V Use equation w nRTan 2 1 Must be at constant temperature lf Pex is constant W PexV2 V1 I Energy 17 rema Energy U il This is the total energy of the system It consists of 393 The energies from motion of all molecules translational energy rotational energy and vibrational energy 3 Bond energy angle energy the angle made between 3 atoms as the outer two vibrate and dihedral angle energy between 4 angles arranged into 2 planes v Nonbonded interactions between atoms more than 5 atoms apart including van der Waals interactions and electrostatic interactions quotIl Energy is a state function which means that it is a physical property which only depends on the state of the system and is not reliant on the path by which the state was reached The change in energy is calculated by the nal energy minus the initial energy The 81 unit for energy is joules but it is also often measured in calories 1 cal 4184 J Energy is an extensive property which means that it is reliant on the amount of bee molecules in the system 9 Since there are so many forms of energy the energy of a system cannot be exactly calculated We can only nd the change in energy by using A U q w q gt 0 when the system absorbs heat and q lt 0 when the system releases heat w gt 0 when the system has work done to it and w lt 0 when the system does work For an in nitesimal charge the equation used is dU dq dw For PV work AU q fv f Pede At constant volume A U qV 0 This equation is used for bomb calorimetry I Enthapy H quotIL H U pV il Like energy enthalpy cannot be calculated only the change in enthalpy can be eeeee ILL It is also an extensive property L The SI unit is joules
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