Question

Three 3−L flasks, fixed with pressure gauges and small valves, each contain 7 g of gas at 271 K. Flask A contains H2, flask B contains He, and flask C contains CH4. Rank the flask contents in terms of:

(e) density.

A > B > C

A > C > B

B > C > A

B > A > C

C > B > A

C > A > B

A = B = C

(f) collision frequency.

A > B > C

A > C > B

B > C > A

B > A > C

C > B > A

C > A > B

A = B = C

Answer 1

(e) Density

A = B = C

Density is given by the formula: Density = Mass/ Volume. Now mass of all three gases is same i.e. 7 grams and also the volume of the three flask A, B and C is same i.e. 3 L. Therefore, density comes out to be same for the three flasks.

(f) collision frequency

A > B > C

The number of collisions depends on both the speed and the distance between gas molecules.

Since molar mass of hydrogen is the smallest among the three gases it will have the maximum no. of molecules as well as the greatest speed, so collisions will occur more frequently between hydrogen molecules than between helium molecules. Again, since Helium has lower mass than methane CH4, its collision frequency will be greater than CH4.