HEM 1031-PRTIE EXM II - LSS - SPRING 2017 NSWER KEY 1. balloon contains 1.30 L of helium at standard temperature and pressure (STP). t 3 atm pressure, what is the volume of the balloon (assuming no change in temperature)? ) 0.300 L ) 3.90 L ) 329 L ) 0.433 L 2. Which of these values is a specific heat capacity? ) 2 J / K ) 3.2 J / mol K ) 15.3 J / kg K ) 32 K / J g 3. What product would you expect to form upon mixture of aqueous solutions of barium chloride and sodium sulfate? ) aso4 (s) ) Nal (s) ) as (s) ) No reaction For problems 4-6, refer to the unbalanced equation 6H12O6 (s) + O2 (g) H2O (l) + O2 (g) 4. If 180.2 g of 6H12O6 reacts with excess oxygen at STP, what volume of carbon dioxide will form? ) 30.03 L ) 1081 L ) 22.4 L ) 134.4 L 5. In a separate experiment, 4 moles of oxygen gas are consumed upon reaction with an unknown amount of 6H12O6. What pressure of carbon dioxide would result from this reaction at 25.0 if captured in a 250 L vessel? ) 391 atm ) 0.587 atm ) 0.391 atm ) 0.0329 atm 6. The reaction described by the chemical equation above is best described as ) an endothermic reaction ) an exothermic reaction ) a thermal reaction ) a heat-absorbing reaction 7. block of hot iron (s,iron = 0.444 J / g ) of unknown mass is dropped into an insulated cup filled with 100 ml vegetable oil (density of oil, 0.93 g/ml; s,oil = 2.00 J / g ). If the temperature of the oil increases 60, and the temperature of the iron decreases by 60, what is the mass of the hot iron block? ssume the iron and oil are thermally isolated from everything else. ) 419 g ) 25.1 kg ) 186 g ) Not enough information
For questions 8-10, consider a coffee-cup calorimeter, which thermally isolates a reaction from the laboratory environment while allowing the reaction to occur at constant pressure. The cup contains 300 ml H2O (density of water, 1.00 g/ml; s,water = 4.18 J / g ). 0.920 g piece of sodium metal is dropped into the water and reacts completely, resulting in the reaction below. 2 Na (s) + 2 H2O (l) H2 (g) + 2 NaOH (aq) 8. If the temperature of the water increases from 25.0 to 35.0, what is Hrxn for the reaction per mole of sodium? ) 1.25 x 10 4 J/mol ) - 1.25 x 10 4 J/mol ) - 3.13 x 10 5 J/mol ) 3.13 x 10 5 J/mol 9. alculate the volume of hydrogen gas generated (assume STP).. 0.448 L ) 0.896 L ) 1.79 L ) none of these 10. The reaction is endothermic. ) True ) False For questions 11-13 use the following chemical equation. gno3 (aq) + K2SO4 (aq) ( ) + (_) 11. Which of the following are the expected products from this reaction? ) gso4 (aq), K2NO3 (aq) ) g2so4 (aq), KNO3 (s) ) g2so4 (s), KNO3 (aq) ) gso4 (aq), KNO3 (aq) 12. Which are the spectator ions? ) g +, SO4 2- ) g +, NO3 - ) K +, NO3 - ) K +, SO4 2-13. t the beginning of the reaction, 0.10 moles of gno3 (aq) is dissolved 100 ml, along with the exact amount of K2SO4 needed for a complete reaction. When the reaction is finished, which of the following describes the resulting solution? ssume all of the starting material is consumed. ) 0 M KNO3 (aq) ) 1 M KNO3 (aq) ) 1M K2NO3 (aq) ) 2M KNO3 (aq) 14. 500 ml of a Na3PO4 solution has a concentration of 3.2 M. The solution needs to be diluted to 1.0 M. How much water should be added? ) 1.6 ml ) 6.4 L ) 1.6 L ) 1.1 L
15. ry ice (solid carbon dioxide, stored at -78 ) is placed in a balloon. The balloon is sealed, and stored on a lab bench at room temperature. s the dry ice warms it becomes gaseous carbon dioxide, which expands the balloon. If the balloon is the system (including the gas and carbon dioxide inside of it), the signs of q and w are ) +q, -w ) q, +w ) +q, +w ) q, -w 16. The energy stored in a battery is an example of ) Thermal energy ) Potential energy ) Kinetic energy ) none of these is correct 17. Which of the following is NOT a strong acid? ) HNO3 ) Hl O4 ) H2O3 ) H2SO4 18. gas can be expected to demonstrate non-ideal behavior at ) large volumes ) high temperatures ) low pressures ) high pressures 19. alculate the urms for a molecule of chlorine gas at 300 K. ) 325 m/s ) 459 m/s ) 2.10 x 10 5 m/s ) 45.6 m/s For questions 20-22, consider the reaction O2 (g) + 2 H2 (g) 2 H2O (l) 20. alculate the number of oxygen molecules that will react with 2.0 L of hydrogen stored at 0 and 760 torr. ) 6.1 x 10 24 ) 7.61 x 10 21 ) 2.7 x 10 22 ) 6.0 x 10 23 21. mixture of oxygen and hydrogen gas is prepared such that no reactant will remain at the end of the reaction. What is the mole fraction of hydrogen in this mixture? ) 0.33 ) 0.67 ) 1/2 ) 1 22. Given the mole fraction determined in question 21, what is the partial pressure of hydrogen if the total pressure is 800 torr? ) 540 torr ) 270 torr ) 800 torr ) 400 torr 23. ecause of the law of conservation of energy, for a system at constant volume, ) qsystem = -qsurroundings ) Esystem = Esurroundings ) Hsystem = Hsurroundings ) ll of the above 24. gas has a molar mass of 32 g/mol. What is its density at STP? ) 0.7 g/l ) 22.4 g/l ) 1.4 g/l ) 2.3 g/l
25. Which gas is the least dense at 300 K and 1.2 atm? ) oxygen (O2) ) helium (He) ) nitrogen (N2) ) xenon (Xe) For questions 26-28, consider a reaction performed in a bomb calorimeter. 0.050 moles of a hydrocarbon compound undergoes combustion, yielding a temperature increase of 12.6. The calorimeter has a heat capacity (including a water bath and calorimeter walls) of 900 J /. 26. What is the sign of the work done by the system in the bomb calorimeter? ) positive ) negative ) w = 0 27. What is the Ecombustion per mole of the unknown compound? ) - 230 kj/mol ) - 11 kj/mol ) - 570 J/mol ) - 340 kj/mol 28. ased on your answer to question 27, what is the sign of Hcombustion? ) positive ) negative ) w = 0 29. Which equation represents the net ionic equation for the reaction of potassium sulfide with strontium acetate? ) K2S(aq) + Sr(2H3O2)2 (aq) K(2H3O2) (aq) + SrS (s) ) S 2- (aq) + Sr 2+ (aq) SrS (s) ) 2K + (aq) + S 2- (aq) + Sr 2+ (aq) + 2 (2H3O2) + (aq) 2K + (aq) + 2 (2H3O2) + (aq) + SrS (s) ) 2K + (aq) + 2 (2H3O2) + (aq) K(2H3O2) (s) 30. Which of the gas molecules has the highest rate of effusion (assuming the same conditions of temperature and pressure)? ) 14 N2 ) 15 N2 ) 16 O2 ) 18 O2
Useful information and equations vogadro s Number = 6.022 x 10 23 mol -1 0 = 273 K 1 atm = 760 mmhg = 760 torr R = 0.08206 (atm L)/(mol K) R = 8.314 J/(mol K) volume of 1 mole of gas at STP = 22.4 L