P Chem : Study guide
P Chem : Study guide CHEM 3423
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This 3 page Study Guide was uploaded by Nicole Takam on Sunday October 4, 2015. The Study Guide belongs to CHEM 3423 at University of Oklahoma taught by Dr. Chaubin Mao in Summer 2015. Since its upload, it has received 87 views. For similar materials see Physical Chemistry in Chemistry at University of Oklahoma.
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Date Created: 10/04/15
Study Guide First Law The Energy of a system is constant That is AU qheat absorbed by the systemw work done on the system Second Law It is impossible for an engine to perform work by cooling a portion of matter to a temperature below that of the coldest part of the surroundings This can be studied using the carnot cycleThe operation of engines in which energy is continuously extracted from an environment which is at the same T or lower T eg a ship on the water could not be driven by abstracting heat from the surrounding water Third law Entropy changes become zero at the absolute zero temperature TOK provided that the states of system are in thermodynamic equilibrium Entropies of all perfectly crystalline substances must be the same at TOK Convention assigning a value of zero to the entropy of every crystalline substance atTOK Ideal vs real gas Ideal gases are gases for which Z 1 and the equations of state can be applied when the gases have high temperatures and Low pressure Those which deviate from the ideal gas behavior are called real gases Reversible process means maintaining equilibrium in an infinitely slow process For this process to occur Psystem Pext on time So if Psystemi Pext the process is irreversible Isolated vs closed systems In an isolated system there is no ow of heat or matter between the system and the surroundings For a closed system there is no matter transfer but energy can be transferred between the system and the surroundings 0 State functions Certain macroscopic properties have fixed values for a particular state of the system For instance 1g of a vessel of water at T 25 degrees Celsius and P 1 bar Once the state of the system is specified by giving some values to the state functions values of the state functions are fixed That is if P T n are known then Volume is fixed These quantities specify the state of the system and are called state functions or state variables For example mass Pressure temperature volume etc Whenever at these conditions water is in the same state the energy of the molecules is the same When the state of any system is changed the state function depend on only the initial and the final states and not on the path taken Work and heat for different processes From the rst law AU qheat absorbed by the systemw work done on the system v2 Reversible PV work wrev I P dV V1 Enthalpy H U PV Heat Capacities dqv aU CV E d T 3LT at constant volume dq 8 H Cp 5 d T 3LT p at constant pressure a U For ideal gases PV NRT and a V T 0 at constant temperature For Isothermal reversible compression of 1 mol of an ideal gas v2 Wrev E qrev V 1 Z Adiabatic process P1 V1 A V P2V2 A V Thermodynamic quantities enthalpy H U PV It is a state function entropy S It is the amount of heat ow per unit temperature It is a state function and therefore path independent quantity d5 dqrev T where dqrev is the amount of heat absorbed in an isothermal and reversible process in which the system goes from one state to another and T is the absolute temperature at which the process is occurring It is extensive thus depending on the amount of material Internal energy U It is involves the kinetic motion of the molecules the potential energy due to the interaction between the molecules kinetic and potential energy of the nuclei and electrons Within the individual molecules Gibbs energy G G H TS Helmholtz energy A A U TS Constant V and T dA 0 and at constant T and P d6 0 Need to know how to calculate their changes A for different processes ideal gas solid liquid Heat capacities Cpm Cvm for gas solidliquid Second Laws dqrev B AS T For any completely any reversibly cycle A520 If any part of the cycle is irreversible ASlt0 according to Clausius Entropy of mixing of ideal gases per mole of mixture AS mix Rx1ln x1 x2ln x2 x mole fractions Carnot39s Thm The work done by the system during the cycle divided by the work that would have been done if all the heat absorbed at the higher T had been converted To work Ef ciency is unity 100 only when Tc is absolute OK The ef ciency of all reversible cycles operating between temperatures T h and T c is the same Ef ciency TH Tc TH Conditions for Equilibrium Any spontaneous process AS totalAS surroundings ASsystem gt 0 Equilibrium AS surroundings ASsystem 0 Systems tend to reduce G ie move toward a state of minimum Gibbs energy dGltO Fugacity and activity Need to know the different equations
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