1. Define molarity and give the symbol for this unit. Do the same for mass % (a.k.a. % w/w).

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1 CHM 112 Study Guide I Chap & 11.1 & 11.3 Sp Closed book. Write your name on the back of the last page & your initials on the back of the other pages. 2. Show calculations and logic throughout to receive full credit. 3. Make appropriate use of significant figures and units. 1. Define molarity and give the symbol for this unit. Do the same for mass % (a.k.a. % w/w). 2. What is the mole fraction of K 2 S in a solution made by dissolving 2.65 g of K 2 S in ml of H 2 O? Assume the density of H 2 O is g/ml. 3. How would you prepare an aqueous solution that is m in NH 4 Cl? What is the NH 4 Cl concentration in wt % of this solution? 1

2 4. Given these data for the reaction of ClO 2 with OH! : Initial rate 2ClO 2 (aq) + 2OH!! (aq) ÿ ClO 3 (aq) +! ClO2 (aq) Exp# [ClO2 ] (M) [OH! ] (M) (M/s) x 10! x 10! x 10! x 10!3 Be sure to explain the logic for your answers. a) Write a general rate law for the reaction. b) Use the initial rate data to write the specific rate law consistent with the data. Make sure you solve to obtain a numerical value for k. c) Write a chemical rxn. for the reactant side of the rate limiting step in the rxn. mechanism. d) Calculate the initial rate of the reaction at M 2ClO 2 and M OH!. 2

3 5. Iodine-125 is a product of some reactions occurring in nuclear reactors and was released into the atmosphere in nuclear reactor incidents at Three Mile Island in the US and at Chernobyl in the Ukraine. Humans were exposed to significant levels of 125 I during this time. 125 I decays with first order kinetics and a rate constant of x 10!6 min!1. a) What is the half-life (in days) of 125 I? b) If a person ingested some 125 I, what percentage of the amount the ingested would be left after four half lives? (Assume 125 I is removed from the body only by radioactive decay.) c) If an individual ingested 542 ng of 125 I 18.0 years ago how much would be left in their body today (make same assumption as in b)? What percentage of the originally ingested 125 I is this? 6. The decomposition of nitryl chloride, NO 2 Cl is believed to occur by the following mechanism: k 1 Step 1 NO 2 Cl ÿ NO 2 + Cl k 2 Step 2 Cl + NO 2 Cl ÿ NO 2 + Cl 2 a) Write a balanced equation for the overall reaction. b) What is the molecularity of each of the elementary steps? c) Write the predicted rate law for the overall reaction if the first step is rate limiting. 3

4 7. Give the Arrhenius equation and define each of the variables. 8. Write equilibrium constant expressions for the following reactions: a) 2 HCl (g) W H 2(g) + I 2(g) b) CH 4(g) + 2H 2 S (g) W CS 2(g) + 4 H 2(g) 9. Shown below is a balanced equation for the decomposition of H 2 S to form H 2 and S 2. a) Write an equilibrium constant expression for the reaction. b) Given the equilibrium concentrations: [H 2 S] = M, [H 2 ] = M, and [S 2 ] = !3 M, calculate the numerical value of K eq. c) Assume the equilibrium is perturbed. When equilibrium is reestablished, the following concentrations are observed: [H 2 ] = M and [S 2 ] = M. Calculate [H 2 S] under these new conditions. d) What can you say about the forward and reverse reaction rates when the system is at equilibrium? e) What can you say about the forward and reverse rate constants, whether the system is at equilibrium or not? 2 H 2 S(g) W 2 H 2 (g) + S 2 (g) 4

5 k f 10. Consider a general, single-step reaction of the type M W N + Q. Show (derive) the k r equilibrium constant expression. State clearly (and non-cyclically) the conditions under which the equilibrium constant may be employed and indicate any aspects of the problem that are by definition Does addition of a catalyst to a reaction system change the value of K c for the reaction? Does addition of a catalyst change the rate constants (k f and k r values) for the reaction? Use a reaction progress diagram (also called potential energy profile in your text) based on the equilibrium described in problem #9 to support your answers. Indicate what energetic features of the diagram relate to the equilibrium constant and what features relate to the rate constants. 12. Give the definition of a Brønsted-Lowry base. 5

6 13. Give the molecular formula of 3 strong acids. 14. Predict the products of the following reaction. Identify the acid and base reactants, as well as their conjugates on the product side. C 2 O 4 2! + H 2 O ÿ 15. Calculate the ph and [OH! ] in M HNO Calculate the [H 3 O + ], [OH! ], [OBr! ], [HOBr] in a solution containing M hypobromous acid (HOBr). For HOBr, K a = 2.0 x 10!9. 6

7 17. Calculate the ph of M Na(CH 3 CO 2 ) (aq) (sodium acetate). K a for acetic acid = !5. Supplemental information. A Periodic Table and electronegativity chart. Table atm = 760. mm Hg K w = !14 R = J'KCmol R = (LCatm)/(molCK) 1 kgcm 2 's 2 = 1 J 1eV = 1.60 x 10!19 J EC = K x =!b ± (b 2! 4ac) ½ 2a 7