The different molecules that make up the air in a room have on average the same kinetic energy. how does the speed of the different air molecules depend on their masses?
(i accidentally put this under the wrong subject)

The formula for kinetic energy is KE=1/2(mv²).  Since both mass and velocity are multiplied by each other, particle with a larger mass needs to be moving slower than a particle with less mass if both have the same kinetic energy. You can think of it as 2KE/m=v² or 2KE/v²=m, If you increase the mass the velocity needs to decrease to keep the same KE value.

I hope this helps.  Let me know in the comments if anything is unclear.

Yes, endothermic means it turns cold. and some chemical changes include change of tempature.