The average speed of a perfume vapor moclecule at room temp may be about 300 m/s?

Question

but you'll find the speed at whicj the scent travels across the room is much less. Why?

Answer 1

Just imagine yourself in a desolate square. If you run from one end to the other at say 15km/hr, you will perform the task in no time.

Now imagine yourself running at the same speed, in the same square, when this is jam packed with people! You might keep your speed, but due to the collisions and zig-zagging (and the inevitable insults from the ones you hit), it will take much longer for you to reach the other end.

The molecule behaves in the same manner. It might have a substantial speed, but the fact that it is continously colliding with other molecules means that the rate of diffusion will be comparitively slow.

Answer 2

There is so much open space in a room for the vapor to move to. Not only that, but you can't smell one molecule of the perfume, you need quite a few to be able to pick up the scent, and at the same time it's trying to reach equilibrium with the room. Wow, I sound like a science nerd lol.

Answer 3

The motion of the perfume molecules have no preferential direction...they move around in a random-like motion...they are not necessarily drawn to a certain spot at 300 m/s, the molecules have to diffuse their way across the room.

Also, air molecules (N2, O2, ...) are moving around too. Perfume molecules will collide with air molecules...a lot...and this continuous collision process affects how far and fast a perfume molecule can move. The molecules are colliding, bouncing around, traveling every which way...all of this slows the propagation of the scent across the room.

Answer 4

You're confusing the molecular average velocity of a single molecule with the velocity of the group (or "ensemble") of molecules of perfume.