Grossmont College Chemistry 141 Exam 2 Fall 2016 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 The pressure exerted on a sample of a fixed amount of gas is doubled at constant temperature and then the temperature of the gas in kelvins in double at constant pressure What is the final volume of the gas a The final volume of the gas is four times the initial volume b The final volume of the gas is one fourth the initial volume c The final volume of the gas is one half the initial volume d The final volume is twice the initial volume e The final volume of the gas is the same as the initial volume 2 3 4 states that the volume of a gas varies inversely to the pressure on the gas when temperature and number of moles are kept constant PV constant a Avogadro s law b Boyle s law c Charles law d Gay Lussac s law e Dalton s law Assuming ideal behavior which of these gas samples has the greatest volume at STP a 1 g H2 b 1 g O2 c 1 g Ar d 1 g CH4 e all of the above have the same volume 5 What is the measurement shown by the calipers a 24 mm b 27 4 cm c 28 4 cm d 29 cm e 30 4 cm 6 For which should the standard heat of formation Hf be zero at 25 C a b c d e 7 oxygen gas O2 g ozone gas O3 g atomic oxygen gas O g all of the above none of the above For a process at constant volume a q 0 w 0 E 0 Page 1 of 7 Grossmont College Chemistry 141 Exam 2 Fall 2016 Name Date Instructor Diana Vance b c d e w 0 and E q w 0 and H q w 0 and E H none of the above 8 For the reaction I2 g I2 s H 62 4 kJ at 25 C then a H vap 62 4 kJ mol b H vap 62 4 kJ mol c H sub 62 4 kJ mol d H sub 62 4 kJ mol e b and c 9 A quantized variable a can be continuously varied b can only assume certain values c consists of photons d is extremely small e is a state function 10 Which subshell letter corresponds to an 8 lobed pattern a s b p c d d f e more than one answer 11 How many electrons does an f orbital contain a 2 b 6 c 7 d 10 e 14 12 Page 2 of 7 Grossmont College Chemistry 141 Exam 2 Fall 2016 Name Date Instructor Diana Vance 13 Part 2 Short Answer 14 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 15 1 State whether each of the following samples of matter is a gas If there is not enough information for you to decide write insufficient information 5 points a A material is in a steel tank at 100 atm pressure When the tank is opened to the atmosphere the material suddenly expands increases its volume by 1 16 Not a gas A gas would expand to an infinite volume b A 1 0 mL sample of material weighs 8 2 g 17 Not a gas A density of 8 2 g mL is typical of a solid c The material is transparent and pale green in color 18 Insufficient information d Nitrogen oxygen and helium at room temperature and pressure 19 Gas e One cubic meter of material contains as many molecules as 1 0 m3 of air at the same temperature and pressure 20 Gas 21 2 At an underwater depth of 250 ft the pressure is 8 38 atm What should the mole percent of oxygen in the diving gas be for the partial pressure of oxygen in the gas to be 0 21 atm the same as it is in air at 1 0 atm 6 points 22 P O 0 21 atm 0 025 23 PO Ptotal O O P total 8 38 atm 24 O2 0 025 100 2 5 O2 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 2 2 2 2 Page 3 of 7 Grossmont College Chemistry 141 Exam 2 Fall 2016 Name Date Instructor Diana Vance 3 You have a gas one of the three known phosphorus fluorine compounds PF3 PF5 and P2F4 To find out which you decide to measure its molar mass 12 points a First you determine that the density of the gas is 5 60 g L at a pressure of 0 971 atm and a temperature of 18 2 C Calculate the molar mass and identify the compound DRT 40 MM P g L atm 5 60 0 08206 18 2 273 15 K L mol K 41 MM 0 971 atm g L atm 5 60 0 08206 291 3 5 K L mol K 42 DRT g g MM 137 884463 138 P 0 971 atm mol mol 43 The molar mass is closest to that of P 2F4 which has a molar mass of 137 94 g mol 44 b To check the results from part a you decide to measure the molar mass based on the relative rates of effusion of the unknown gas and CO2 You find that CO2 effuses at a rate of 0 050 mol min whereas the unknown phosphorus fluoride effuses at a rate of 0 028 mol min Calculate the molar mass of the unknown gas based on these results 45 mol 2 0 050 rate1 MM 2 rate1 2 min g g g MM 2 MM 1 44 009 140 3348214 140 rate2 MM 1 rate 2 mol mol mol mol 0 028 min 46 This is consistent with the results from part a 47 4 A 13 8 g piece of zinc is heated to 98 8 C in boiling water and then dropped into a beaker containing 45 0 g of water at 25 0 C When the water and metal come to thermal equilibrium the temperature is 27 1 C 15 points a What is the specific heat capacity of zinc q q out 48 q water q zinc 49 m water c water T water m water c water T water m zinc c zinc T zinc c zinc 50 m zinc T zinc 51 J J 45 0 g 4 184 27 1 25 0 45 0 g 4 184 2 1 g g J c zinc 0 399599782 0 40 g g 13 8 g 27 1 98 8 13 8 g 71 7 b If the molar heat capacity of zinc at 300 K is 25 45 J mol K what is the percent error J 1 mol Zn 1K J J 0 389250864 0 3893 52 …