Thermal Physics: Gases Flashcards
Define pressure of a gas.
the force per unit area that the gas exerts normally on a surface.
State Boyle’s law.
Draw graph.
for a fixed mass of gas at constant temperature, pV=k.
A graph of p-V is a curve that tends towards each axis.
(isothermal change)
What is an ideal gas?
A gas that obeys Boyle’s law.
State Charles’ law.
Draw graph.
for a fixed mass of gas at constant pressure, V/T=k.
Graph is straight line through 0K.
(isobaric change)
When work is done to change the volume of a gas, energy must be transferred by heating to keep p constant. How is this done (give eq)?
Work is done by the gas on the piston. W = p ΔV
State the pressure law.
For a fixed mass of gas at constant volume, p/T = k.
Brownian motion:
Through a demonstration, was shown unpredictable movement of molecules of gas (random w/ diff speeds). Motion of each particle is bc of?
Motion of each smoke particle is because it’s bombarded unevenly and randomly by individual air molecules. Particles ∴ experience forces due to these impacts, which change its magnitude and direction randomly.
Observe existence of molecules and atoms.
Air: fast moving, random motion, air size «_space;smoke size
3 empirical/experimental laws combine to give:
pV = nRT, for fixed mass of an ideal gas.
For an ideal gas at constant pressure, its density is inversely proportional to what?
To its temperature.
Speed of individual molecule changes when it collides with another gas molecule. But distribution stays the same as long as temp doesn’t change.
(c rms)
If temp increases what happens? (graph: # molecules with speed v-speed v)
As temp increases, c rms increases ∴ distributiuon curve becomes flatter and broader bc the greater the temp the more molecules there are moving at higher speeds.
Kinetic theory was:
a) devised by observation and experiment
b) devised by theory and math
b) devised by theory and math
pV=1/3 Nm c rms^2,
where N = number of molecules and m = mass of each molecule
Kinetic theory: underlying assumption (5):
1- point molecules.
2- don’t attract.
3- random motion
4- elastic collisions
5- negligible collision time
1- point molecules.
1- molecules are point molecules. the volume of each molecule is negligible compared w/ the volume of the container.
2- don’t attract.
2- they do not attract each other. If they did, the force of their impacts on the container’s surface would be reduced.
3- random motion
3- they move about in continual random motion.
