CHM 142 Exam Questions and Answers Latest Update Graded A+

CHM 142 Exam Questions and Answers Latest Update Graded A+ The density of a gas is 1.676 g/dm3. What is the mass (in kg) of 188 m3 of this gas? - Answers 315.1 KG What is the mass of oxygen in a 77.06 g sample of cadmium phosphate, Cd3(PO4)2? - Answers 18.7g A sample of metallic zinc weighing 18.96 g is placed in an aqueous solution containing 0.212 mol of silver nitrate, causing the following reaction to occur Zn(s) + 2AgNO3(aq) → 2Ag(s) + Zn(NO3)2(aq) What is the maximum mass (in grams) of silver that could form? - Answers 22.9 how many moles of the excess reactant will remain unreacted when 1.327 mol of NH3 and 2.175 mol of O2 react to form NO and H2O. 4NH3(g) + 5O2(g) → 4NO(g) + 6H2O(g) Assume 100% yield. - Answers 0.516 Find the molarity (in mol/L) of the Ba(OH)2 solution that required 40.84 mL of a 0.227 M aqueous solution of HCl to completely neutralize a 25.00 mL sample of Ba((OH)2. - Answers 0.185 Given the following thermochemical equation ⅓N2(g) + H2(g) ⇌ ⅔NH3(g) ∆Hrº = -32.01 kJ/mol find ∆Hrº (in kJ/mol) for the following reaction. 2NH3(g) ⇌ N2(g) + 3H2(g) - Answers 96 Given ∆Hrº's for the following three reactions 2C(graphite) + 2H2(g) → C2H4(g) ∆Hrº = 52.1 kJ/mol H2(g) + ½O2(g) → H2O(g) ∆Hrº = -235 kJ/mol 2C(graphite) + 3H2(g) + ½O2(g) → C2H5OH(g) ∆Hrº = -271 kJ/mol find ∆Hrº for the following reaction. C2H4(g) + H2O(g) → C2H5OH(g) - Answers -88.1 Given the following thermochemical reaction find ∆Hº (in kJ) when 3.112 g of C6H6(l) is burned. 2C6H6(l) + 15O2(g) → 12CO2(g) + 6H2O(l) ∆Hrº = -6536 kJ/mol - Answers -130 A fixed amount of gas has a volume of 429.1 mL at 50.52 ºC. What volume (in mL) will the gas occupy if it is cooled to 24.96 ºC at constant pressure? - Answers 395.2 The volume of a sample of helium at 743.1 torr and 23.02 ºC is 268.3 mL. What will the pressure (in torr) of this sample be if the temperature is changed to 35.74 ºC and the volume is changed to 230.4 mL? R = 0.082057 L atm K-1 mol-1 = 62.364 L torr K-1 mol-1 1 atm = 760 torr - Answers 902.5 Which of the following substances will be miscible with water? - Answers propanol, C3H7OH What is the molality (in mol/kg) of a solution of heptane (C7H16) in hexane (C6H14) that is 16.7% heptane by mass? - Answers 2.001 The vapor pressure of pure benzene at 30 ºC is 119.1 torr. Calculate the vapor pressure of benzene (in torr) above the solution of naphthalene in benzene if the mole fraction of naphthalene is 0.15. - Answers 101.2 Compared to pure water, the solution of KCl in water has I. higher boiling point II. higher vapor pressure III. higher freezing point. - Answers only I Which of the following aqueous solutions will have the highest boiling point? - Answers 0.50 m FeCl3 Arrange the following aqueous solutions in order of increasing freezing points: A: 0.10 m CaCl2; B: 0.10 m KCl; C: 0.30 m NaCl. Note: the solution with the lowest freezing point should be first and the one with the highest freezing should be last - Answers C < A < B Determine the boiling point elevation of a solution prepared by dissolving 0.436 mol of a nonvolatile, nonionic solute in 277 g of carbon tetrachloride (Kb = 5.02 ºC/m). - Answers 7.9 If the following aqueous solutions were separated by semipermeable membrane from pure water, in which case the highest pressure would have to be applied to stop the osmosis? - Answers 0.125 M Fe(NO3)3 Find the osmotic pressure (in atm) of seawater in which the total concentration of particles is 1.15 M if the temperature is 21.18 ºC. - Answers 27.8 A solution containing 0.726 g of an unknown substance in 35.8 mL of aqueous solution has an osmotic pressure of 1.18 atm at 22.11 ºC. What is the molar mass (in g/mol) of the unknown substance? - Answers 416.4 Consider the following reaction 5Br-(aq) + BrO3-(aq) + 6H+(aq) → 3Br2(aq) + 3H2O(l) Which one of the following is not a valid expression between various rates involving reactants and products? - Answers -∆[Br-]/∆t = (3/5) ∆[Br2]/∆t Consider the following reaction N2(g) + 3H2(g) → 2NH3(g). The concentration of NH3(g) increases from 24.04 mM to 79.24 mM in 15.5 s. What is the average reaction rate (in mM/s)? You Answered - Answers 1.781 Consider the following reaction 4NH3(g) + 7O2(g) → 4NO2(g) + 6H2O(g) If O2(g) is being consumed at a rate of 80.5 µM s-1, what is the rate of the reaction (in µM s-1)? - Answers 11.5 The rate law for a reaction that involved three reactants was investigated by using the initial-rate method. When the concentration of reactant A was doubled the rate of the reaction was doubled. When the concentration of reactant B was tripled the rate of the reaction was tripled. When the concentration of reactant C was halved the rate of the reaction was not affected. What is the rate law for this reaction? Correct! - Answers Rate = k[A][B] Find the rate constant for the reaction between A and B given the following data: Trial[A], (M)[B], (M)Rate (M/s)10.2410.4330.22520.2410.8660.45030.7230.4332.025 - Answers 8.95 M-2 s-1 The rate constant for a chemical reaction was determined to be 0.475 M-2 s-1. What is the overall order of this reaction? - Answers 3 Find the half-life (in s) of the reaction