Chemical Kinetics TURN ON SPECs NOW!

First things first… Safety: Put bags away Goggles Lab Jacket Gloves Basic Reactants! LAB! Warm up Spec 20

Reaction Rate The rate of reaction may be defined (and measured) as the rate of disappearance of any reactant, ot the rate of appearance of any product. CH 4(g) + 2 O 2(g) → CO 2(g) + 2 H 2 O (l)

Rate Expression The mathematical equation showing how reaction rate depends on reactant concentrations is called the rate expression.

Crystal Violet Lab We are studying the reaction of crystal violet to sodium hydroxide and how they are related to rate law and reaction order crystV + (aq) + OH - (aq) > crystV-OH(aq) (purple) (colorless) Complete Rate Law: Rate = k [crystV+] x [OH-] y Because NaOH is 1000x more concentrated, doesn’t change much over time so we are actually looking at the Modified Rate law: Rate = k' [crystV+] x where k' = k [OH-] y

Beer-Lambert Law We are measuring the reaction rate by using a UV-vis spectrometer to measure the color change over time Obtaining the % Transmittance Absorbance = -log(%T/100) Absorbance is proportional to Concentration

Procedure 1. Warm up Spec 20 for 15 min. 2. Set to 540nm 3. Two standard concentrations will be analyzed: M NaOH – two trials M NaOH – two trials 4. Blank: Blank Spec with clean test tube and NaOH sol’n (around ¾ full) 5. Mix crystal violet solution: Use one drop of dye in NaOH solution, invert quickly to mix, and record at time zero. 6. Record your %T: Record %T readings every 30 seconds for 15 minutes

How to blank a spec – write down! Blank a spec before every trial 1. Without test tube in spec 20, turn the dial until % transmittance is 0 2. Fill a test tube ½-3/4 full with blank solution (the NaOH soln) 3. Put test tube in spec 20, make sure white tag is not blocking the light, and close the door opening 4. Turn the dial until %T is 100

Due by end of lab Clean up the lab station and hood closest to your station Turn in your lab notebook with following: purpose, equipment/chemicals, procedure, observations/new equipment, filled out data table.

Lab Report Due in TWO weeks (2/27/2012) Typed, given to me in hard copy during class.

Lab Report Contain Contains following in order: Title, Data tables, Graphs, Calculations, Conclusion/Discussion, References Title Page: Name, Date, Lab Partner, Sect. Data Tables ( excel) Raw data (%T vs T) Calculated data (Abs vs. T)

Graphs 6 graphs total (excel) 3 graphs of A vs. T (0 order), ln A vs. T(1 st order), 1/A vs. T(2 nd order) for Trial M NaOH Find the linear trendline y=mx+b and regression Choose which graph has the most linear line Linear graph will det. your overall reaction order For Trial M, Trial M, Trial M….1 graph per trial Make linear graphs for each trial. You determined which reaction order graph was most linear based upon the one for Trial M Find linear trendline y=mx+b and regression for each trial.

Calculations – typed or blue/black ink Show one example calc how convert %T to Absorbance You are trying to find k and x and y and complete rate law: Rate: k [crystV+] x [OH-] y X order (crystal V) You will determine order from which graph was most linear A vs. T (0 order) ln A vs. T(1 st order) 1/A vs. T(2 nd order)

K’ You get from slope of linear graph from the trendline. If you have a linear graph from…. 0 order: k’ = -m 1 st order: k’ = -m 2 nd order: k’ = +m Get average k’ for M and average k’ for 0.05 M

Find y order (NaOH) Comparing two equations (k1' / k2' ) = ([OH-] 1 / [OH-] 2 )y k1’ = M k’, k2’ = 0.05 M k’ [OH-] 1 = M, [OH-] 2 = 0.05 Y = ln((k1' / k2' )) / ln(([OH-] 1 / [OH-] 2 )) Find k Plug in values k’, [OH-], and y: Get Average k from ALL four trials

Complete your rate law, plug in your k, x, and y value you found previously Rate = k [crystV+] x [OH-] y

Discussion/Analysis 1 page, double spaced What values did you find for your results aka what rate law did you get and how get it Is it precise, accurate? Error analysis – how did your errors affect your data (did it increase, decrease values?) More questions and prompts you can find on the pbwiki