(Solved): 15. A 300 .-mL sample of hydrogen, \( \mathrm{H}_{2} \), was collected over water at \( 21^{\circ} ...

15. A 300 .-mL sample of hydrogen, \( \mathrm{H}_{2} \), was collected over water at \( 21^{\circ} \mathrm{C} \) on a day when the barometric pressure was 748 torr. What mass of hydrogen is present? The vapor pressure of water is 19 torr at \( 21^{\circ} \mathrm{C} \). A) \( 0.0186 \mathrm{~g} \) B) \( 0.0241 \mathrm{~g} \) C) \( 0.0213 \mathrm{~g} \) D) \( 0.0269 \mathrm{~g} \) E) \( 0.0281 \mathrm{~g} \) 16. Which of the following gases will have the smallest rate of effusion? \( \mathrm{H}_{2}, \mathrm{O}_{2}, \mathrm{He}_{2} \mathrm{~N}_{2}, \mathrm{CO} \) A) \( \mathrm{H}_{2} \) B) \( \mathrm{He} \) C) \( \mathrm{N}_{2} \) D) \( \mathrm{O}_{2} \) E) \( \mathrm{CO} \) 17. What is the ratio of the average speed of \( \mathrm{SO}_{2} \) molecules to that of oxygen molecules at 298 K? B) \( 1: 1 \) C) \( 2: 1 \) D) \( 2: 2 \) E) None of the above 18. If \( q=-29 \mathrm{~kJ} \) for a certain process, that process A) occurs rapidly. B) is exothermic. C) is endothermic. D) cannot occur. E) requires a catalyst. 19. How much heat is liberated at constant pressure if \( 0.796 \mathrm{~g} \) of calcium carbonate reacts with \( 56.4 \mathrm{~mL} \) of \( 0.229 \mathrm{M} \) hydrochloric acid? \[ \mathrm{CaCO}_{3}(s)+2 \mathrm{HCl}(a q) \rightarrow \mathrm{CaCl}_{2}(a q)+\mathrm{H}_{2} \mathrm{O}(t)+\mathrm{CO}_{2}(\mathrm{~g}) ; \Delta H^{\circ}=-15.2 \mathrm{~kJ} / \mathrm{mol} \] A) \( -0.0982 \mathrm{~kJ} \) B) \( -12.1 \mathrm{~kJ} \) C) \( -0.121 \mathrm{~kJ} \) D) \( -3.48 \mathrm{~kJ} \) E) \( -0.219 \mathrm{~kJ} \)