Advanced Chemistry Practice Problems Kinetics!!!

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Wilfred Simpson
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1 Name Advanced Chemistry Practice Problems Kinetics!!! Period 1. The gas-phase reaction of nitric oxide and bromine yields nitrosyl bromide: 2NO(g) + Br 2 (g) -> 2NOBr(g) The rate law is rate=k[no][br 2 ]. a. What is the order with respect to NO b. What is the order with respect to Br 2? c. What is the overall reaction order? 2. The reaction of hydrogen and iodine monochloride is first order in H 2 and second order in ICl. H 2 (g) + 2ICl(g) -> 2HCl(g) + I 2 (g) a. What is the rate law? b. What are the units of the rate constant? 3. Use the following data to answer the following questions about the decomposition of N 2 O 5. [N 2 O 5 ] (M) Log [N 2 O 5 ] 1/[N 2 O 5 ] Question 4 Graph 1 Question 4 Graph 2 Log [N2O5] /[N2O5] Series1 a. What is the order of the reaction? Please explain how you arrived at your answer! b. What is the rate law for this reaction? c. What is the value of the rate constant? d. What is the molarity of N 2 O 5 after 265 s? e. How long does it take for the concentration of N 2 O 5 to drop to M? 4. Nitrogen dioxide decomposes to nitric oxide and molecular oxygen: 2NO 2 (g) -> 2NO(g) + O 2 (g) Use the following data to answer the following questions.

2 [NO 2 ] (M) Log [NO 2 ] 1/[NO 2 ] Question 3 Graph 2 Question 3 Graph 1 1/[NO2] (1/M) Log [NO2] a. Is the reaction first order or second order? Explain your answer. b. Calculate the value of the rate constant. c. What is the concentration of NO 2 at t=25 minutes? d. What is the half-life of the reaction when the initial concentration of NO 2 is M? f. What is t 1/2 when [NO 2 ] o is M? 5. What step in a reaction mechanism is the rate-determining step (fastest or slowest)? 6. What is the Arrhenius equation and what can you find out about a reaction from the equation? 7. Draw two potential energy profiles, one for a catalyzed reaction and one for an uncatalyzed reaction. Label activation energy, change in energy, and the x and y axis. Practice Problems - Chemical Equilibrium!!! 1. What are the units for K? 2. Write the equilibrium constant for the following reactions: a. 2NO(g) + Br 2 (g) -> 2NOBr(g) K = 2.2 x 10 4 b. H 2 (g) + 2ICl(g) -> 2HCl(g) + I 2 (g) K = 8.6 x Using the reactions in Question 2, when the reactions come to equilibrium does the equilibrium mixture contain mostly reactants or mostly products? a. b. 4. Once again, use the reactions in Question 2 to write the expression for K p for each reaction. a. b.

3 5. Write the expression for K c for each reaction in Question 2. a. b. 6. The equilibrium constant K = 7.9 x 10 5 for the reaction: 2NO(g) + O 2 (g) <=> 2NO 2 (g) a. Given the concentrations of NO, O 2 and NO 2 are 0.25 M. Find the reaction quotient (Q c ). b. Is the reaction at equilibrium? If not, in which direction does the reaction proceed? 7. The equilibrium constant K = 1.2 x for the reaction: H 2 (g) <=> 2H(g) a. Using the K are the reactants or the products favored? b. What is the molar concentration of H atoms if [H 2 ] = 0.12 M at equilibrium? 8. Given K = 2.06 for the reaction: CO(g) + H 2 O(g) <=> CO 2 (g) + H 2 (g) a. What are the equilibrium concentrations of CO 2 and H 2 O if the initial concentrations of reactants are 0.25 M? 9. The equilibrium constant K = 1.7 x 10-3 for the reaction: N 2 (g) + O 2 (g) <=> 2NO(g) a. If the initial concentrations of the reactants are 0.20 M for N 2 and 0.50 M for O 2, what are the concentrations of NO, N 2 and O 2 when the reaction mixture reaches equilibrium? 10. For the following reaction; N 2 (g) + 3H 2 (g) <=> 2NH 3 (g) a. Using Le Chatelier s principle predict the direction of the reaction if you increase [N 2 ] or [H 2 ] Thermochemistry/Chemical Energy Practice Problems 1. Calculate (in Joules) the work done by a chemical reaction if the volume increases from 3.2 L to 3.4 L against a constant external pressure of 3.6 atm. What is the sign of the energy change? 2. What is the sign of H for an exothermic reaction? For an endothermic reaction? 3. Under what circumstances are H and E nearly equal? 4. Used in welding metals, the reaction of acetylene with oxygen has H = kj. How much P-V work is done in kj and what is the value of E in kj for the reaction of 5.25 g of acetylene at 2 atm if the volume change is -2.8 L? C 2 H 2 (g) + 5/2O 2 (g) -> H 2 O(g) + 2CO 2 (g) H = kj

4 5. Titanium metal is used as a structural material in many high-tech application such as in jet engines and bicycles. What is the specific heat of titanium in J/(g C) if it takes 89.8 J to raise the temperature of 33.0 g block by 5.21 C? 6. Describe Hess's law, why does it work, and what is a compound's standard heat of formation? 7. Calculate H f for benzene, C 6 H 6, in kj/mol from the following data: 2C 6 H 6 (l) + 15 O 2 (g) -> 12CO 2 (g) + 6H 2 O(l) H = kj H f (CO 2 ) = kj/mol H f (H 2 O) = kj/mol 8. If it takes 1200 J of energy to inflate a balloon from 1L to 2L against an external pressure of 0.9 atm, is more energy required to inflate it or to do the PV work against the atmosphere? Show how much more through calculations. 9. Vinyl chloride (H 2 C=CHCl), the starting material used in the preparation of polyvinyl chloride, is prepared by a two step process that begins with the reaction of Cl 2 with ethylene to yield ethylene dichloride: Cl 2 (g) + H 2 C=CHCl(g) -> ClCH 2 CH 2 Cl(l) H = kj/mol Is the reaction endothermic or exothermic? 10. When 1.50 g of magnesium metal is allowed to react with 200 ml of 6 M HCl, the temperature rises from 25 C to 42.9 C. Calculate H in kj for the reaction, assuming that the heat capacity of the calorimeter is 776 J/ C, that the specific heat of the final solution is the same as that of water [4.18J/( g C)], and that the density of the solution is 1.00 g/ml. Gas Practice Problems 1. Carry out the following conversions! a atm to pascals b inches to atm 2. Why is atmospheric pressure less at the top of mountain than at sea level (~1 atm)? 3. Briefly describe the following gas laws - use equations as much as possible! a. Boyle s Law: b. Charles Law: c. Avogadro s Law: 4. What conditions are defined as standard temperature and pressure? 5. What are two characteristics/assumptions about real gases that cause the predictions of the ideal-gas law to vary from actual values?

5 6. If 2.5 g of the vapor of a volatile liquid is able to fill mL flask at 91 C and 745 mm Hg: a. What is the molar mass of the liquid b. What is the density of the vapor under these conditions? 7. The liquids used in the Vapor Pressure Lab were insoluble in water. What effect would be seen if the liquids tested by this method were soluble in water? For example, ethanol is fairly volatile but is also completely miscible with water in all proportions. 8. What is the difference between effusion and diffusion? 9. Briefly describe Dalton s law of partial pressure! 10. A typical high-pressure tire on a road bicycle has a volume of 375 ml and a pressure of 130 psi (lb/in 2 ) at 25 C. Suppose the rider filled the tire with helium to minimize weight. What would be the mass of helium in the tire? 11. If 15.0 g of CO 2 gas has a volume of 0.30 L at 300 K, what is its pressure in mm Hg? 12. How many moles of air are there in the lungs of an average adult with a total lung capacity of 4.0 L? Assume that the person is at 1.0 atm pressure (On a nice Hawaiian beach) and has a normal body temperature of 98.6 C. Use your own pulse if necessary! Liquids and Solids Practice Problems 1. Label each of the following forces as either intermolecular or intra molecular! a. Hydrogen bond b. Covalent bond c. Ionic bond d. London dispersion e. Dipole-dipole 2. What type of force explains the unique properties of water; such as surface tension and capillary action? 3. A topaz crystal has a lattice spacing (d) of 1.5 A (1A = 1.x10-10 m). Calculate the wavelength of X-ray that should be used if = 16 (assume n=2). 4. Based on their properties, classify each of the following as to the type of solid it forms (molecular, network, or ionic): a. diamond b. NaCl

6 c. Cl 2 d. C 2 H 4 e. Graphite 5. Steel is formed by mixing iron and carbon. Carbon fills the gaps between the iron atoms making steel stronger by preventing the iron atoms from moving. What type of alloy is steel? Interstitial or Substitutional 6. How does the vapor pressure of a pure liquid vary with temperature? 7. Metals are ductile, malleable, and good conductors of heat and electricity. Describe or give an example of the following characteristics. a. Ductile = b. Malleable = c. Conductors of heat/electricity = 8. Calculate the vapor pressure of propanol at 53 C if the heat of vaporization is 50 kj/mol and the vapor pressure is 15 C at 10 torr. 9. On a phase diagram be able to identify the following! a. Identify the triple point. b. Identify the normal boiling point. c. Identify the normal freezing point. d. Identify the critical point. e. Which phase is denser, solid or liquid?

(a) graph Y versus X (b) graph Y versus 1/X

(a) graph Y versus X (b) graph Y versus 1/X HOMEWORK 5A Barometer; Boyle s Law 1. The pressure of the first two gases below is determined with a manometer that is filled with mercury (density = 13.6 g/ml). The pressure of the last two gases below