DETERMINATION OF AN EQUILIBRIUM CONSTANT平衡常数测定.ppt

* DETERMINATION OF AN EQUILIBRIUM CONSTANT Experiment #5 There are two aspects to chemical reactions which though, interrelated, are dealt with as two separate topics. The first of these is the study of the reaction from it initiation to a point where the system seems to undergo no further change, called chemical kinetics. The deals with the system after all “apparent change” have stopped, and is called chemical equilibrium. A + 3B 2C+ 2D Reversible reactions When reactants are mixed in stoichiometric quantities, they are not completely converted to products. Reactions that do not go to completion and that can occur in either direction are called reversible reactions. aA + bB cC+ dD forward backward What is chemical equilibrium? Chemical equilibrium exists when two opposing reactions occur simultaneously at the same rate 2Hl(g) H2(g)+I2(g) Kinetics Equilibrium Apparent change in concentration of reactants and products No apparent change in concentration of reactants and products Equilibrium, an analogy Amount of water being pumped in = Amount of water being pumped out nAA + nbB nCC+ nDD Kforward kbackward Equilibrium Constant At equilibrium At equilibrium Upper case Lower case What is equilibrium concentration? Concentration of a reactant or a product left after the equilibrium has been established. Mathematically expressed: A comparison of rate law and equilibrium constant Rate law Equilibrium constant nAA + nbB nCC+ nDD kforward kbackward nAA + nbB nCC+ nDD k unidirectional bidirectional k is called the rate constant and has units that depend on order. m and n are the order of the reaction due to A and B respectively. They have to be determined experimentally Keq is unitless nAA, nb, nCC and nD are stoichiometric coefficients of A,B,C and D respectively. obtained from the balanced chemical reaction Experiment Determin