P-CHEM Final Flashcards
pressure is —– proportional to volume
inversely
volume is ——– to temperature
proportional
in PV=nRT what is the purpose of the R constant?
to ensure the units are the same on both side of the equation
what is the R constant?
8.314 j/mol*k
in the Dieterici equation of state what are the units of b?
m^3/mol
in the Dieterici equation of state what are the units of a?
J∙m^3/mol^22
why is PV=NRT not a perfect equation?
It doesn’t describe all gas behavior. Thus, it is an approximation of most gas behavior.
What 2 implications make a gas a perfect gas?
The gas molecules do interact with one another. The gas atoms do not collide and the molecules themselves do not have volume
is the van der Waals “a”
parameter positive or negative for all gases?
always positive
What is the role of the van der Waals “a”
parameter
to lower the pressure of a real gas to values lower than that of a perfect gas
van der Waals “a”
parameter lowers the pressure of the real gas to larger extent if the —- is smaller
hint
p real- p perfect = -(n^2*a)/ V^2
volume
The van der Waals a parameter is associated with the gas molecules interactions with each other. How does this influence the pressure of a real gas?
Interactions between gas molecules lowers the pressure. Thus, a smaller volume means more interactions and the real pressure is significantly lower than predicted by PV=nRT
What does the b parameter in the van der Waals equation account for ?
The volume of the gas molecules themselves
What does the compressibility factor describe about a gas ?
How closely the gas of interest behaves like a perfect gas
What variable of the PV=nRT equation does the compressibility factor analyze?
The pressure
if Z < 1 than the pressure of the real gas is —– than that of a perfect gas
less than aka the observed pressure is too low
if Z > 1 than the pressure of the real gas is —– than that of a perfect gas
greater than aka the pressure of the real gas is too high
How does the b(volume) parameter of the Van der Waals equation affect the numerical magnitude of the Z(compression factor)
The b parameter increases Z because the B parameter is always positive
How does the a(attractive forces) parameter of the Van der Waals equation affect the numerical magnitude of the Z(compression factor)
The a parameter decreases the value of the compression factor
Are Van der Waals parameters dependent on temp?
No
What is residual volume?
involves low pressure or high volume conditions
per mold volume of real gas - per molar volume of perf gas
What is the residual volume of a perfect gas
0
work done (dw=+) on a cylinder system requires a —- in volume
decrease (aka compression) via increase in applied exterior pressure
work done by a cylinder system requires a — in volume
increase ( aka expansion ) via decrease in applied exterior pressure
compression and expansion of a piston stop when the —- pressure is equal to the —– pressure are equal
interior and exterior
Work is inexact bc it is —— dependent
path
during an isothermal compression, heat flows — the system to maintain temp constant
out of
during an isothermal expansion heat flows — the system to maintain temp constant
into
heat and work are —- because they are path dependent
inexact
what can Euler’s test be used to determine?
if a differential is exact or inexact
Internal energy
is the energy of
a single molecule
Internal energy is a state function, and its
differential ∂U is —-
exact aka path independent
Every atom in every molecule has at minimum —- degrees of freedom
3
A linear molecule has the capability to do — additional rotations
2
a non linear molecule is capable of —- rotations
3
——- do not practically count towards a
molecule’s internal energy
hint rotations, vibrations, translations
vibrations
under isothermal conditions what is the change in internal energy(du=?)
0J because the temp is constant
what is the change in heat under isothermal condtions?
dq=-dw
is CP,m greater than or lesser than CV,m
greater than
what is the change in heat of adiabatic system?
dq=0J because heat transactions with the exterior environment are not possible to maintain the temp constant
Does an adiabatic system experience a change in internal energy
