20.3 The Kinetic Theory of gases Flashcards
(19 cards)
what does it mean by the gas laws were experimental or empirical
devised by experiments and observations
what can the experimental gas laws be explained by assuming
gas comsists of molecules moving about at random, continually colliding with container walls
each impact causes a force on the container
the force of many impacts is the cause of the pressure of the gas on the container walls
how can boyles law be explained
the presssure of a gas at constant temperature is increased by reducing its volume because the molecules travel less distance between imacts on the walls due to reduced volume
therefore more impacts per second and so the pressure is greater
how can the pressure law be explained
the pressure of a gas at constant volume is increased by raising its temperature. the average speed of the molecules is increased by raising the gas temperature. therefore the impacts of the molecules on the container walls are harder and more frequent so pressure is raised as a result
what are the speeds like in an ideal gas
the molecules in an ideal gas have a continous spread of speeds
the speed of an individual molecule changes when it collides with another gas molecule but the distribution stays the same as long as the temperature doesn’t change
what is the root mean square speed of the molecules Crms
Crms= c1^2+c2^2…../N rooted
C repersents the individual speeds
N = the number of molecules in the gas
what happens to the Crms when temperature increases
when temp is raised the molecules move faster on average. the root mean square speed of the molecules increase. the distribution curve becomes flatter and broader because the greater the temp, the more molecules that are moving at higher speeds
what assumptions must be made about molecules in a gas in order to dervive the kinetic theory equation
1) the molecules are point molecules. The volume of each molecule is negligible compared to the volume of the gas
2) they dont attract eachother. if they did the effect would be to reduce the force of their impacts on the containers surface.
3)They move about in continual random motion
4)The collisions they undergo with eachother and with the container surface are elastic collisions
5) Each collision with the container surface is of much shorter duration than the time between impacts
how do you find the speed for a molecule with different velocity components
pythagoras
what is the change of momentum of a molecule when coliding with a surface
final momentum - initial momentum
(-mu)-(+mu) = -2mu
what is the time between successive impacts on a face given by
t = total distance to the opposite face and back / x compoment of velocity (look at graph)
2lx/u
pv =
1/3 N m crms^2
crms ^2 =
u1^2 +v1^2…../N
for an ideal gas what is its internal energy only due to
the kinetic energy of the molecules of the gas
how to find the mean kinetic energy of a molecule of gas
1/2 m crms^2
how to find the mean kinetic energy of a molecule of an ideal gas
3/2 KT
how to find the total kinetic energy of n moles of an ideal gas (internal energy)
3/2 n R T
how to find crms^2
Crms = root 3RT/M
when answering a uestion about ehy theres pressure or why it increases in an object which equations should you reference
p=f/a f = the rate of change of momentum
