【都灵理工】化学基础_12 equilibrium

Chemistry for engineering equilibrium Silvia Bodoardo1CONTENTS•definition•equlibrium constant•homogeneous and heterogeneousequilibrium•Le Chatellier principleChemistry for engineering equilibrium Silvia Bodoardo2Chemistryfor engineering equilibrium Silvia Bodoardo3After a certain time the concentration of all species does notchange any more The reaction can occur in both directionsChemistry for engineering equilibrium Silvia Bodoardo 4The products and the reactants formation proceeds at the same rate. We are in dynamic equilibrium conditions. In general, all chemical reaction are reversible process that canbe carried put in both directions. N 2+ 3H 22NH 3equilibriumWhen, during a chemical reaction, the reactants and productsconcentration remain constant in time, we are in chemicalequilibrium conditions. reactants productsChemistry for engineering equilibrium Silvia Bodoardo5010”70”80”50”60”40”20”30”[NO2]N2O4 2 NO2timeChemistry for engineering equilibrium Silvia Bodoardo6N2O4(g) 2 NO2(g)Initial pressure(atm) equilibrium pressure(atm) Chemistry for engineering equilibrium Silvia Bodoardo7Rate law for the forward reaction(v1)N2+ 3H22NH3And that for the reverse reaction(v2)2NH3N2+ 3H2v1= k1[H2]3[N2]v2= k2[NH3]2At equilibrium v1= v2k1[H2]3[N2] = k2[NH3]2Chemistry for engineering equilibrium Silvia Bodoardo8Chemistry for engineering equilibrium Silvia Bodoardo 9k 1[NH 3]2k 2[H 2]3[N 2]K c is the equilibrium constant (it depends only onthe temperature)== K c For gases:K p =pNH32p H23p N2N2O4(g) 2 NO2(g)Chemistry for engineering equilibrium Silvia Bodoardo10In general:aA+bB cC+ dD K c= [C]c[D]d[A]a[B]bK c = K p.(RT) -∆ν(c+d) -(a+b) =∆νRemember thatpV=NRT N/V =conc.N/V = p/(RT)Chemistry for engineering equilibrium Silvia Bodoardo11Chemistry for engineering equilibrium Silvia Bodoardo 12For heterogeneousequilibria, the equilibrium constantdepends only on gaseous species.Example:CaCO 3(s)CaO (s)+ CO 2(g)K c = [CO 2]K p = p CO2Equilibria before presented are all ho mogeneous equilibria , i.e reactants and products in the same phase.When reactants and products are pesent in different phve heterogeneous equilibria.Chemistry for engineering equilibrium Silvia Bodoardo 13Heterogeneous equilibria[CaO] [CO 2]K c ’= -----------------[CaCO 3]K c = [CO 2] K p = pCO 2pCaO pCO 2K p ’= -----------------pCaCO 3examplesBaO2(aq)+ H2SO4(aq) BaSO4(aq)+ H2O2(aq)3 H2(g) + N2(g) 2 NH3(g)NiO(s)+ H2(g) Ni(s)+ H2O(g)PCl5(g)PCl3(g)+ Cl2(g)[PCl3] [Cl2] pPCl3pCl2K c= ------------K p= ------------[PCl5] pPCl5Chemistry for engineering equilibrium Silvia Bodoardo14Chemistry for engineering equilibrium Silvia Bodoardo 15CaCO 3(s)CaO (s)+ CO 2(g)K p = pCO 2Chemistry for engineering equilibrium Silvia Bodoardo 16Le Chatellier PrinciplePCl 5(g)PCl 3(g)+ Cl 2(g)[PCl 3] [Cl 2] pPCl pCl 2K c = ------------K p = ------------[PCl 5] pPCl 5If a system isdisturbed, itwill undergo a change that shifts its equilibrium position in a direction that reduces the effect of the disturbance.Chemistry for engineering equilibrium Silvia Bodoardo17Mobile EquilibriumDisturbing an equilibrium:ËChange of reactants and/orproducts concentration ËChange of temperatureËchange of volume or pressureof the systemChemistry forengineering equilibrium Silvia Bodoardo 18Change of concentrationreactants productsIfproducts concetration is reduced, the equilibrium shift to right();If reactants concetration is reduced, the equilibrium shift to left( ).Chemistryfor engineering equilibrium Silvia Bodoardo 19Chan ge of conce ntrati onreactants products+ heatIn this case an increase of temperaturecauses a shift of the equilibrium towards left.A lowering of temperature causes a shift toproducts formation.Chemistry for engineering equilibrium Silvia Bodoardo20Chemistry for engineering equilibrium Silvia Bodoardo21Change of volume and pressureIt influences only gaseous equilibria. An increase of pressure makes shift the reaction in the direction in which there is a lowering of the molecules number. A decrease of pressure has the opposite effect.Chemistry for engineering equilibrium Silvia Bodoardo22。