Three vessels of equal capacity have gases at the same temperature and pressure. The first vessel contains helium (monoatomic), the second contains fluorine (diatomic) and the third contains sulfur hexafluoride (polyatomic). The correct statement, among the following is :
- The root mean square speed of sulfur hexafluoride is the largest
- All vessels contain unequal number of respective molecules
- The root mean square speed of molecules is same in all three cases
- The root mean square speed of helium is the largest
Answer
(4) The root mean square speed of helium is the largest
Solution
Same V, P and T by Avogadro's hypothesis all vessels contain an equal number of molecules, so (2) is wrong.
vrms = 3RTM at the same T, vrms 1 M
Molar masses: He = 4, F2 = 38, SF6 = 146 g mol-1
Helium (lightest) has the largest rms speed.
Answer: (4)