真空计算题_28页.ppt

单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,*,例题,例,3.,在一抽成真空的容器中单独放有,NH,4,Cl(s),，,在,340,o,C,时分解反应,NH,4,Cl(s)=NH,3,(g)+,HCl,(g),的平衡压力,P,1,=104.6kPa,；,同样条件下，若单独放有,NH,4,I(s),分解反应,NH,4,I(s)=NH,3,(g)+HI(g),的平衡压力,P,2,=18.85kPa,。求,NH,4,Cl(s),与,NH,4,I(s),两种纯固态物质同时存在，加热到,340,o,C,，,当上述两个反应都达到平衡时，系统的总压为多大,?,设,HI(g),不分解，两个盐类不形成固态溶液。,1,Answer 1,NH,4,Cl(s)alone:NH,4,Cl(s)=NH,3,(g)+HCl(g),P(NH,3,)=,P(HCl,)=P,1,/2,NH,4,I(s)alone:NH,4,I(s)=NH,3,(g)+HI(g),P(NH,3,)=P(HI)=P,2,/2,2,When NH,4,Cl(ammonium chloride)and NH,4,I(ammonium iodide)coexist in the system,the partial pressure(,分压,)of ammonia(NH,3,)gas must accord with both two equilibrium mentioned above.If the partial pressure is P(NH,3,)for NH,3,(g),P(HCl,)for,HCl(g,)and P(HI)for HI,So,(1),(2),and P(NH3)=,P(HCl)+P(HI,)(3),The answer is P(total)=P(NH,3,)+P(HCl)+P(HI)=106.3kPa,3,Answer 2,Let x and y denote the amounts of,HCl,and HI when the two equilibrium coexisted in the reaction system.So the amount of NH,3,in the system must be x+y and the total amounts of three gas is 2(x+y).Thus,the partial pressure of NH,3,is,and,4,(we can see the partial pressure of P,(NH3),=,P,(HCl,),+P,(HI),),X=30.83y P(total)=106.3kPa,5,Key problem in this example,1.The partial pressure is a intensive variable(,强度变量）,and the amount of species is extensive variable(,广度变量）,2.Equilibrium constant for heterogeneous reactions(,复相反应的平衡常数,),3.The calculate rule for the,equilibria,coexisted in a system(,同时平衡的计算原则）,6,Review,1 The criterion of a spontaneous chemical,reaction,2 The description of an equilibrium of,reaction,3 The isothermal(constant temperature),equation,7,Review,1 Several symbols,1The Gibbs energy of a reaction system,G,2The reaction Gibbs energy:,r,G,m,=(G/,),P,T,3 The standard reaction Gibbs Energy,4 is the Gibbs energy of mixing A and B,5 Standard Gibbs energy of formation,8,2 Several relations:,1 relation of reaction Gibbs energy(,r,G,m,)to the chemical potentials of the species,r,G,m,=,products,-,reactants,2 The standard,equilibrium constant(K)and the standard reaction Gibbs energy,=-RT In,K,o,3,general expression for,r,G,m,at an arbitrary stage of the reaction,r,G,m,=+RT In Q,9,Review,5,thermodynamic equilibrium constant,(,热力学平衡常数,)can expressed in terms of activities(or,fugacities,):,K for Perfect gas reaction,solution reaction and heterogeneous reaction has different form.,6 in terms of standard Gibbs energies of formation,10,The content for this class,1The standard Gibbs energy of reaction in solution,2 The response of,equilibria,to the conditions,1 How,equilibria,respond to pressure?,2The effect of inert gas on,equilibria,11,The content for this class,3 Le,Chateliers,principle,4The response of,equilibria,to temperature,(van t Hoff equation),3 The coexist equilibrium,12,1 The standard Gibbs energy of reaction in solution,(1),Because the value of standard Gibbs energy formation(,标准生成吉布斯自由能,)is for a pure species,so the value of the standard reaction Gibbs energy(,反应的标准吉布斯自由能变,)indicated that the standard state of each reactant and product is in the pure state.,13,The standard state for the species in solution reaction maybe not the pure state.,(1)The solution need not distinguish,solvent(,溶剂,)and solute(,溶质,),Equation(1)can be used to calculate the,14,(2)The solvent and solute need distinguish,and the solution is dilute(,稀溶液,).,The standard state of each reactant and product is,c,i,=1mol.dm,-3,and the solution submit Henrys law hypothetical.,15,Example,Calculate the ionization constant,（,电离常数）,for benzoic acid C,6,H,5,COOH in solution at 298 K.,C,6,H,5,COOH(aq.)=C,6,H,5,COO,-,(aq.)+,H,+,(aq,.),Given that for C,6,H,5,COOH in the solid state,and,for C,6,H,5,COO,-,(C=1.0 mol.dm,-3,).The solubility of C,6,H,5,COOH in water is 0.02787 mol.dm,-3,at 298K.,16,2 The response of,equilibria,to the conditions,1,How,equilibria,respond to pressure,(P234):,The standard equilibrium constant is independent of the pressure,but the equilibrium composition depends on the pressure,.(,压力对化学平衡的影响，实际上并非是对平衡常数的影响，而是指对平衡移动的影响）,17,Le,Chateliers,principle:,A system at equilibrium,when subjected to a disturbance,responds in a way that tends to minimize the effect of the disturbance.,The principle implies that if a system at equilibrium is compressed,then the reaction will adjust so as to minimize the increase in pressure.,18,2 effect of inert gas(,惰性气体,)on equilibrium,1.If an inert gas is added to an equilibrium mixture of gases,at constant temperature and volume,there is no effect on the equilibrium.,Because the addition of an inert gas leaves the molar concentrations of the original gases unchanged,as they continue to occupy the same volume.,19,2.If adding an inert gas,at constant temperature and pressure,which has the same effect as lowering the original gas partial pressure.,If ,the addition of an inert gas at constant pressure reduces the sum of the partial pressure of the reactants and products,and the reaction shifts to the left to compensate for this.,20,Example,At 1273 K and a total pressure of 30.4,atm,the equilibrium in the reaction CO,2,(g)+C(s)=2CO(g)is such that 17 mol%of the gas is CO,2,.,(a)What would be CO,2,if the total pressure were 20.3,atm,?(b)What would be the effect on the equilibrium of adding N,2,to the,21,Example,reaction mixture in a closed vessel until the partial pressure of N,2,is 10,atm,?If the reactant gases contain a mole of N2 in addition to 1 mole of CO2,what is the equilibrium extent of reaction at 30.4,atm,?(d)At what pressure of the reactants will 25%of the gas be CO,2,?,22,4 The response of,equilibria,to temperature,According to Le,Chateliers,principle,a system at equilibrium will tend to shift in the,endothermic direction,if the temperature is raised,while the equilibrium tend to shift in the,exothermic direction,if the temperature is lowered.,23,The van t Hoff equation,The van t Hoff equation is an expression for the effect of temperature on the standard equilibrium constant,K,o,.,Here is the,standard reaction,enthapy,at the temperature T.,24,the value of K at different temperature,General,the,integral(,积分,)of Vant Hoff Equation is used for gas reaction which the pressure is low.,(1)If varies only slightly with temperature over the temperature range of interest,the,integral,of equation from T,1,to T,2,yiels,25,(2)If depends on temperature,Specially,when the,heat capacities(,热容）,of reactants and products is the mean value,the value of is constant,then,26,3 The effect of initial composition on equilibrium,For example,consider the equilibrium for the production of methanol from CO and H,2,:CO(g)+2 H,2,=CH,3,OH(g),27,3 The effect of initial composition on equilibrium,The value of K at 500 K is 0.00623.(a)A gas stream containing,equimolar,amounts of CO and H,2,is,paased,over a catalyst at 101.3,kPa,.What is the extent of reaction at,equilibrium?(b,)If the initial composition is 2 mole H,2,and 1 mole CO,what is the equilibrium extent?,28,