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1、Definition of Physical Chemistry,Physical chemistry stands in the same relation to the subdivisions of chemistry in which philosophy stands toward all the sciences. Its main object is to unify thought within the science of chemistry; therefore, it might well be named, the “philosophy of chemistry” -
2、 S.L. Bigelow, 1912,The Properties of Gases,Equations of State,Bulk Variables,Volume - m3 Pressure - Pa Temperature - K Composition - moles,Volume,length3 units m3 or cm3 liter = 1000 cm3 molar volume Vm= V/n,1 m,1 m,1 m,Pressure,Force/Area units Pascal = Newton/m2 = Joule/m3 atmosphere = 101325 Pa
3、bar = 100000 Pa mm Hg torr,h,Temperature,thermometryT Volume only for an ideal gas or real gases in the low pressure limit,Composition,moles: niS ni = n mole fraction: xiS xi = 1 partial pressure: piS pi = p,Equations of State,P,V,T, and n are not independent. Any three will determine the fourth. An
4、 equation of state is an equation that relates P,V,T, and n for a given substance. Gases have the simplest equations of state. The simplest equation of state is the ideal gas law, pV = nRT,Ideal Gas Law,p = pressure V = volume n = moles T = temperature R = universal gas contant = 0.08206 L-atm/mol-K
5、,Partial Pressure,pA = partial pressure of gas A V = total volume nA = moles of gas A T = temperature R = universal gas contant = 0.08206 L-atm/mol-K,Daltons Law,The total pressure is the sum of all the partial pressure.,Ideal Gas Model,Molecules may be treated as point masses relative to the volume
6、 of the system. Molecular collisions are elastic, i.e. kinetic energy is conserved. Intermolecular forces of attraction and repulsion have negligible on the molecular motion.,Compressibility,The compressibility of a gas is defined by,If the gas behaves ideally, then Z=1 at all pressures and temperat
7、ures. For real gases, however, Z varies with pressure, and deviates from its ideal value,Argon Compressibility 273 K,Z = pVm/RT,attractive,repulsive,Intermolecular Forces,attractive,repulsive,Taylor Series,Taylor Series Example,Convergence of (1-x)-1,Virial Expansion,Virial Expansion,Relation of p a
8、nd 1/V Expansions,Second Virial Coefficients B,cm3/mole,Virial Expansion,Advantages fits gas data as accurately as desired. uses the ideal gas law as a base. Disadvantages infinite number of terms. virial coefficients are temperature dependent.,van der Waals Equation,repulsion,attraction,van der Waa
9、ls Equation,van der Waals constants,Successive Approximation,“Solve” the van der Waals equation for V. Use an intial estimate to evaluate the right hand side. Use this calculated value of V as a better estimate. Repeat till converged.,Ideal Gas Isotherms,100K,4000K,2000K,1000K,500K,Vm/L,p/atm,van der Waals Isotherms - Ar,Vm/L,p/atm,100K,150K,200K,500K,Critical Constants,Inflection Points,Inflection Points,Carbon Dioxide Critical Isotherm,304 K,Vm /L,p/atm,van der Waals Inflection Point,van der Waals Virial Expansion,