Chem 142 Quiz 1 Spring 2009Name _________Key_______________ ___________________ Instructor: Martin Larter1. For the reaction given below, answer the following questions:5 Br-(aq) + BrO3-(aq) + 6 H+(aq) 3 Br2(aq) + 3 H2O(l)(a) Based on the stoichiometry of the equation what are the relative rates of disappearance and appearance (Δ[X]/Δt) of the reactants and products, respectively?(b) If the rate of appearance of Br2 is 6.33 x 10-4 M/sec, what is the rate of disappearance of BrO3-?2. For the chemical reaction given below:2 HgCl2(aq) + C2O42-(aq) 2 Cl-(aq) + 2 CO2(g) + Hg2Cl2(s)The following initial rates of reactions were determined for the reactant concentrations given:Experiment # [HgCl2] [C2O42-] Initial rate (M/sec)1 0.100 0.20 3.1 x 10-52 0.100 0.40 1.2 x 10-43 0.050 0.40 6.2 x 10-5(a) Find the order of the reaction with respect to HgCl2.(b) Find the order of the reaction with respect to C2O42-.(c) Write the rate law for this reaction.(d) Calculate the value for the rate constant based on the data for experiment #1 and provide the proper units.(e) In another experiment, experiment 4, it was found at t=0 that Δ[C2O42-]/Δt = -5.34 x 10-2 M/sec. What is Δ [HgCl2]/Δt under those conditions?3. The decomposition of phosphine, PH3, follows first-order kinetics.4 PH3 (g) → P4 (g) + 6 H2 (g)The half-life for the reaction at 550 °C is 81.3 seconds. How long does it take for 89.0% of a phosphine sample to decompose?Ln([PH3]/ [PH3]0 )= – ktk = ln2/81.3 sec = 0.00853 s-1([PH3]/ [PH3]0 )= amount remaining 100% -89.0% = 11.0% remainingLn([0.11[PH3]0/ [PH3]0 ) = –0.00853 s-1 (t)t =- ln( 0.11)/ 0.00853 s-1 = 259
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