2) The Kc value for the following equilibrium at 500°C is 49. +114375 liostdrmol/L L -01$125M H2 (g) + I2 (g)= 2HI(g) M.V=meres If 1.50 moles of H2 and 1.50 moles of la are introduced into a 2.00 L flask at 500°C how many moles of HI are present at equilibrium? K. и.] (1.43 3) What would happen to the values you calculated for Kc in the experiment ifthe Beer's Law constant (k) value you used was high (e.g. you used 6,000 M²' when the actual constant had a value of 5,000 M-)? Explain your answer. Revision Determination of an Egquilibrium Constant 69 Objectives: 1) To review Beer's Law and use it to determine the concentration of a complex involved in a chemical equilibrium. 2) To use experimental data to determine an equilibrium constant Background: By now you have had experience viewing what happens during chemical reactions. Many of the reactions we've studied so far in lab go to completion. In other words, wimon the reaction has finished, it is assumed that the reaction has gone as far as it can, consuming at least one reactant completely. It would be more realistic to say that often chemical reactions do not go to the pomit tar one or more reactants are consumed completely. Instead we see that a certain anmount of product forms, and the forward progress of the reaction comes to a halt. "ThiS is not because the reaction stops, but because the reverse reaction is taking place at the same rate as the forward reaction. In other words, equilibrium is established. At equilibrium, the concentrations of reactants and products in a reaction will not change unless something is changed. We can express the equilibrium in mathematical terms through an equilibrium constant, which accounts for all products and reactants in solution. a A tbB >c +dD Kea = c^ Od, In this lab you will be looking at the equilibrium: Fe3+ +SCN= Fe(SCN)²+. The equilibrium constant expression for this reaction is: morancunCof vanes WIT products+ rcactans magnen Both the iron(III) cation (Fe+) and the thiocyanate anion (SCN) are colorless in acidic Rea-7 Ko ramo [Fe(SCN)2+] [Fe3+][SCN-] horw much formed %3D -7 solution, while the thiocyanato iron(III) complex (Fe(SCN)2*)is a deep red. The equilibrium concentration of the complex can therefore be determined by using Beer's Law while the equilibrium concentrations of the reactants can be determined by difference if the initial concentrations before equilibrium are known. Beer's Law states that the absorbance of a solution containing a colored species is directly proportional to the concentration of the colored species. Baen's This relationship can be rewritten as an equation by placing a constant into the equation. The constant is known as absorptivity or molar absorptivity. A = kC %3D M= Absorb mmy %3D (Note that this is a small k and is not the same as Ke!) If Beer's Law is followed, then a plot of absorbance versus concentration should give us a straight line with slope equal to absorptivity. specs Fe 37-) from Fecao 3. recNO;) CSCN 31 -2fnm SN--> from (.