Grossmont College Chemistry 141 Exam 2 Spring 2015 Name Date Instructor Diana Vance Exam 2 Part 1 Multiple Choice 2 points each Directions Please circle the best answer for each of the following questions 1 Toxicity refers to the capability of a substance to a Cause systemic harm to a living organism b Damage an organ in a living organism c Adversely modify a biochemical system d All of the above e None of the above 2 An instrument used to measure atmospheric pressure is called a a barometer b manometer c sphygmomanometer d spectrometer e pressureometer 3 Using the graph below determine the gas that has the lowest density at STP a A b B c C d D e All of the gases have the same density at STP 4 Define vapor pressure a Partial pressure of water in a liquid mixture b Partial pressure of water in a gaseous mixture c Condensation of water d Water dissolved in a liquid e Water molecules 5 For Esys to always be what must be true a q w b q w c w q d w q e none of the above 6 Which statement is false a An exothermic reaction gives heat off to the surroundings b Enthalpy is the sum of a system s internal energy and the product of pressure and volume c Erxn is a measure of heat d Hrxn is the heat of reaction e Endothermic reactions have a positive H 7 Two aqueous solutions are both at room temperature and are then mixed in a coffee cup calorimeter The reaction causes the temperature of the resulting solution to fall below room temperature Which of the following statements is true a The products have a lower potential energy than the reactants b This type of reaction will provide data to calculate Erxn Page 1 of 9 Grossmont College Chemistry 141 Exam 2 Spring 2015 Name Date Instructor Diana Vance c d e The reaction is exothermic Energy is leaving the system during the reaction none of the above statements are true 8 The vertical height of a wave is called a wavelength b amplitude c frequency d area e wavenumber 9 Which of the following quantum numbers describes the size and energy of an orbital a magnetic quantum number b principal quantum number c angular momentum quantum number d spin quantum number e Schr dinger quantum number 10 In which orbital below would an electron on average be farthest from the nucleus a 1s b 4f c 3s d 3d e 2p Page 2 of 9 Part 2 Short Answer Directions Answer each of the following questions Be sure to use complete sentences where appropriate For full credit be sure to show all of your work 1 Use the following data to draw a graph of the volume of helium as a function of temperature for 1 0 mol of He gas at a constant pressure of 1 00 atm How would the graph change if the amount of gas were halved 10 points T K 96 48 24 9 6 4 8 V L 7 88 3 94 1 97 0 79 0 39 V2 L 3 94 1 97 0 99 0 39 0 20 Volume L Charles Law Volume vs Temperature K 9 00 8 00 7 00 6 00 5 00 4 00 3 00 2 00 1 00 0 00 f x 0 08x 0 R 1 1 0 mol of gas Linear 1 0 mol of gas 0 5 mol of gas Linear 0 5 mol of gas f x 0 04x R 1 0 10 20 30 40 50 60 70 80 90 100 Temperature K If the amount of gas were halved the graph would still be linear but the slope would be halved 2 Why doesn t Dalton s Law of Partial Pressures depend on the identity of the gases present 3 points It is assumed that all gas particles are behaving ideally and not interacting with one another If that is true the only difference between particles is associated with their mass Since all of the gases are at the same temperature and have the same average kinetic energy their masses don t have to be taken into account All that matters is all of the different gas particles exert the same force on the walls of the container no matter what their mass 3 An odorous gas emitted by a hot spring was found to diffuse 2 89 times slower than helium 8 points a What is the molar mass of the emitted gas rateHe MM rate He 2 MM MM He rate MM He rate g g 33 4 mol mol b If the gas is found to be hydrogen sulfide what is the percent error in the measurement MM 2 89 2 4 003 observed theoretical 100 theoretical g g 33 4 34 077 mol mol error 100 g 34 077 mol g 0 677 mol error 100 2 g 34 077 mol error 4 Carbon tetrachloride was at one time used as a fire extinguishing agent It has a molar heat capacity cp of 131 3 J mol C How much heat in kJ is required to raise the temperature of 275 g of carbon tetrachloride from room temperature 22 C to its boiling point 77 C 8 points q mc T molJ 77 22 153 823 g C Cl 1 mol C Cl J q 275 g C Cl 131 3 55 mol 153 823 g C Cl 1 mol C Cl 4 q 275 g C Cl 4 131 3 4 4 4 4 4 q 12910 37426 J 1 3 10 J 13 kJ 5 You are given the following data 6 points N2 g O2 g NO g Hrxn 90 3 kJ NO g Cl2 g NOCl g Hrxn 38 6 kJ 2 NOCl g N2 g O2 g Cl2 g Hrxn a Which of the Hrxn values represent enthalpies of formation N2 g O2 g NO g Hrxn 90 3 kJ b Determine Hrxn for the decomposition of NOCl N2 g O2 g NO g Hrxn 90 3 kJ 2 and flip NO g Cl2 g NOCl g Hrxn 38 6 kJ 2 and flip 2 NO g N2 g O2 g Hrxn 180 6 kJ 2 NOCl g 2 NO g Cl2 g Hrxn 77 2 kJ 2 NOCl g N2 g O2 g Cl2 g Hrxn 103 4 kJ 103 kJ 6 Why is it necessary to know the heat capacity of a calorimeter 3 points It is necessary to know the heat capacity of a calorimeter because we need to know how much energy generated or absorbed by the system is required to change the temperature of the surroundings the calorimeter in order to calculate the heat capacity or final temperature of the system in an experiment 7 Aspirin is produced commercially from salicylic acid C7O3H6 A large shipment of salicylic acid is contaminated with boric oxide which like salicylic acid is a white powder The heat of combustion of salicylic acid at constant volume is known to be 3 00 x …