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1、4.1.2 Standard equilibrium constant(K)A large number of experiments show that at a certain temperature,when the reversible reaction reaches equilibrium state,there is a quantitative relationship between the equilibrium concentrations of various substances,which can be expressed by equilibrium consta
2、nt.Standard(relative)equilibrium constant:can be expressed by the relative concentration and the relative partial pressure.The relative pressure:p pp 100 kPa:the standard gas pressure The relative partial concentration:c cc 1.0 molL-1:the standard concentration For gas reaction:aA(g)+bB(g)=gG(g)+dD(
3、g),when the reaction reaches a equilibrium state(PG/P)g(PD/P)d K=(PA/P)a(PB/P)b PG,PD,PA,PB:partial pressure of gas components(G,D,A,and B).PG/P,PD/P,PA/P,PB/P:corresponding to their relative partial pressureStandard equilibrium constant expression:For liquid reaction:aA(aq)+bB(aq)=gG(aq)+dD(aq)CG,C
4、D,CA,and CB:when the reaction reaches a equilibrium state,the concentration of various components(G,D,A,and B),respectively.C=1.0 mol.L-1 CG/C,CD/C,CA/C,and CB/C:corresponding to their relative concentration,respectively.(CG/C)g(CD/C)d K=(CA/C)a(CB/C)bThe following two points should be paid attentio
5、n when writing the equilibrium constant:1.Pure solid,pure liquid and other pure solvents be not written into the expression of equilibrium constant.2Al2O3(s)+3C(s)=4Al(s)+3CO2(g)K=p(CO2)/p 32Al2O3(s)+3C(s)=4Al(s)+3CO2(g)K=p(CO2)/p3Example:1)N2(g)+3H2(g)=2NH3(g)2)1/2N2(g)+3/2H2(g)=NH3(g)3)2NH3(g)=N2(
6、g)+3H2(g)2.The expression of equilibrium constant should correspond to their stoichiometric equation.That is,for the same reaction system,when different stoichiometric equations are expressed,the corresponding equilibrium constants are different.The equilibrium constant must correspond to their stoi
7、chiometric equation 2Cl-(aq)+2H2O(l)=H2(g)+Cl2(g)+2OH-(aq)K=Zn(s)2H(aq)H2(g)Zn2(aq)K=Example:At 1000K,1 mole of SO2 and 1 mole of O2 are put into a 5 L closed container.When the reaction reaches equilibrium state,0.85 mole of SO3 generates.Under these conditions,the chemical reaction formula,as follow:2SO2+O2=2SO3,how much are the partial pressure of each substance in this formula and its K?Solve:2SO2+O2=2SO3ninitial(mol)1 1 neq(mol)1-0.85 1-0.85/2 0.85 pV=nRT p(i)=K=3.38