Two gases, A and B, are together in a balloon. The temperature of the
gases is 25 degrees C and the molecules of gas B have a greater mass
than those of gas A. Which of the following statements is correct?
a. The molecules of gas A have a greater average speed than those of
gas B.
b. The molecules of both gases are moving at the same average speed.
c. The molecules of gas A have a greater average kinetic energy than
those of gas B.
d. The molecules of gas B have a greater average kinetic energy than
those of gas A

Hi teatea!!

Temperature, when measured in Kelvin degrees, is a number that is
directly proportional to the average kinetic energy of the molecules
in a substance.

The kinetic energy of a given molecule
Ek = 1/2.m.v^2

For the average kinetic energy
AvEk = 1/2.m.u^2   , where u is the root-mean-square (rms) speed.

Note that, for the same AvEk, the larger the mass the lower the rms
speed. Thus, as the molecules of gas B have a greater mass than those
of gas A, the rms speed of the molecules of gas A have a greater rms
speed than those of
gas B.

The correct statement is a.

Statements c and d are obviously opposed to the kinetic theory,
because if both gases are at the same temperature, then the average
kinetic energy of the molecules is the same for both gases.

Statement b means that both gases have the same molecular mass; that
is not true because the molecules of gas B have a greater mass than
those of gas A.


Hope this helps.

Regards.
livioflores-ga

---

Clarification of Answer by livioflores-ga on 11 Jul 2003 01:27 PDT

The following lecture will be useful:
"The Kinetic-Molecular Theory of Gases":
http://www.chemistry.ohio-state.edu/~chan/chem121_autumn02/printouts/chan_Lecture_29_doc.pdf

Good luck.
livioflores-ga