Experiment 29 Page 331
Objective To measure the effect of concentration upon the rate of the reaction peroxydisulfate and iodine To determine the order of the reaction with respect to the concentration of the reactants To obtain the rate law of the reaction
Factors that Affect Rates of Reaction 1. Nature of Reactants The reactants must come into direct contact with each other and must collide with sufficient energy to result in a reaction 2. Concentration Changes the number of particles per unit volume 3. Temperature Changes the kinetic energy of the particles (i.e. velocity) which changes the number of collisions in a period of time 4. Catalyst Lowers the activation energy of the reaction while remaining chemically unchanged
Order of Reaction The rate of the reaction may be expressed by: [A] and [B] are the molar concentrations of A and B x and y are the powers which the concentration must be raised to describe the rate k is the specific rate constant for a reaction Independent of concentration and depends only on temperature Once the rate is known the value of k can de calculated
Order of Reaction con’t. Suppose we found that x = 2 and y = 1 for the reaction The rate law would then be: If [B] is doubled (keeping [A] the same)the rate will double If [A] is doubled (keeping [B] the same)the rate will quadruple The powers in the rate law are the order of the reaction The reaction above would be: Second order in A First order in B The overall order is the sum of the exponents or third-order overall
Experimental Procedure Do preliminary experiment on page 335 to observe color change Prepare solution using instructions and set-up on page 335 and 336 Fill seven test tubes with 1 -mL Na 2 S 2 O 3 and put aside Add Ammonium persulfate (NH 4 ) 2 S 2 O 8 to solution as per procedure on 336 and begin timing IMMEDIATELY! The instant the color changes 2x10 -4 mol of S 2 O 8 2- has reacted record time and add 1 -mL Na 2 S 2 O 3 and color will dissapear Record time for color to reappear and repeat for remaining 6 aliquots of Na 2 S 2 O 3 and for solutions 2, 3 and 4
Lab Report Do Calculations on page 337 Plots may be done by hand or spreadsheet Answer all questions and fill out tables on pages 339 and 340 Due next week: Report Sheet for Experiment 29 – page Four plots from the calculation section (one for each solution) Pre-Lab questions for experiments 29 (page 337) and 21 (page 231)