kinetic theory unit 3 Flashcards
ideal gas assumptions
collisions are perfectly elastic, particles bounce of each other and the container without losing any kinetic energy.
the gas molecules exert forces on each other only when they collide.
the gas molecules are so tiny they take up no space at all, molecules themselves have negligible volume.
kinetic theory assumptions
a molecule moves with uniform velocity between collisions.
the motion of the molecules is evenly distributed over all directions.
there is a random distribution of energy among the particles.
the range of intermolecular forces (attractive and repulsive) is small compared to the average distance between the molecules.
ideal gas equation
PV=nRT
units and measurements of the ideal gas equation
P=pressure, Pa, Nm-2 V=volume, m3 n= number of moles, mol R= constant (data booklet) T= temperature, K
general gas equation
p1v1/t1=p2v2/t2
M
molar mass, kgmol-1
Mr
relative molecular/atomic mass
MT
total mass of sample, kg
m
mass of 1 molecule, kg
n
no. of moles, mol
N
no. of molecules
NA
avogadros constant (data booklet)
moles and mass equations need to know (not in data booklet)
M=Mr/1000 (in data. booklet)
n=MT/M (in data. booklet)
n=N/NA
m=M/NA
what is pressure
pressure=force per unit area, P=F/A
break down the total pressure exerted by the gas on the wall
each collision causes a force to be exerted by the molecule on the wall because the molecule experiences a change in momentum m(v-u) as it bounces of the wall and from newtons 2nd law since f= rate of change of momentum the wall must exert a force on the molecule from newtons 3rd law that tells that the molecule exerts an equal but opposite force on the wall. and the total pressure exerted by the gas on the wall is the sum of all these tiny molecular forces that act on it.
molecules experience changes in momentum m(v-u) as it bounces off the wall and since newtons 2nd law where f= rate of change of momentum each collision causes a force to be exerted by the molecule on the wall. also because of newtons 3rd law this tells us that the molecule exerts an equal but opposite force on the wall so the wall must exert a force on the molecule. and then the total pressure exerted by the gas on the wall is the sum of all these tiny molecular forces that act on it.
factors affecting gas pressure
temperature =hotter, greater mean KE per molecule, molecules gain more force(hit harder) and more often.
destiny =more gas molecules per area, increase collisions.
volume =same no. of gas molecules in smaller volume , greater collisions.
all result in more pressure generated(opposite would decrease pressure)
c_2 (c squared bar)
mean square speed, m2s-2
rms
root mean square speed, ms-1
U
sum of KE and PE of objects molecules (ideal gas molecules only have KE and no PE from no intermolecular forces except when are colliding KE=U)
mole
amount t of substance that has the same no. of particles as there are atoms in 12 grams in C12
avogadros constant
number of particles in a mole
