the gas phase Flashcards
inertia
- Inertia is the resistance of any physical object to any change in its velocity.
1atm=
760mmHg
760 mmHg or 1 atm =
1 x 10^5 pa
standard tempurate and pressure is (STP)
273 K ( 0 degrees C) and 1atm
equations for ideal gases assume?
negligible mass and volume of gas particles
AT STP 1 MOLE OF ANY IDEAL GAS occupies
22.4 L
( no matter the type of gas, if 2 gases have the same molar amounts (1 mol, 2 mol …) at the same temp and pressure they will occupy the same volume
ideal gas law
relationship between P, V, n and T
PV=nRT
Avogadro’s principle
special case of ideal gas law!
- P and T constant can relate V and n
n1/V1 = n2/V2
Boyles principle
T and n are constant
P1V1=P2V2
Charles law
P and n are constant
- V1/T1= V2/T2
Gay-Lussacs law
V and n constant
P1/T1= P2/T2
combined gas law
combines boyles, charles and gay-lussacs laws-
P1V1/T1= P2V2/T2
daltons law
total pressure from partial pressures ( add up all partial pressures )
Henery law
the amount of gas dissolved in solution is directly proportional to the partial pressure of that gas at the surface of the solution
[A] = Kh x Pa or [A]i/Pi = [A]f/Pf = Kh
we can define the state of a gas asmple by 4 variables
PVTn
difference between STP (standard temp and pressure) conditions and standard state conditions
STP = 273 K or 0 C and 1 atm - used for gas law calculations
standard state conditions = 298K (25C), 1atm, 1M - are used when measuring stadard enthalpy, entropy, free energy changes and electrochemical cell voltage
what is an ideal gas?
when we do gas questions we assume that the gases are ideal which just means that there are no intermolecular forces and the molecular occupy no volume
when do real gases deviate form this
at high P or low T
R (ideal gas constant) =
- 8.21 x 10^-2 L-atm/mol K
- or may be 8.3 J/K-mols)
- don’t need to memorize but be aware that it can be expressed in two ways (different units)
how to solve ideal gas law questions
- convert al given variables into the appropriate units, solve for x
density
p= PM/RT
mass/volume (g/L)
- we can rearange the ideal gas law (bc it contains volume and number of moles)
MM=g/mol –> mol = g/MM
so n= mass/MM
- to know: density (p)= PM/RT
what is the density of CO2 at 2 atm and 273 C?
- use combined gas law ( 1 and 2 refer to the states of the gas at STP and at conditions in the question)
- P1V1/T1 = P2V2/T2
V1= at STP 22.4L P1= 1atm T1= 273 K
V2= x P2= 2 atm T2= 273 C + 273 = 546 K
arrange equation to solve for V2
find MM of Co2
to find density= MM/L/mol = g/L
What is the MM of a 22.4L sample of gas that has a mass of 225g at 273 C and pressure of 10atm?
(this one is tricky!)
- identity unknown of gas
- think of the values that have been given as V2, P2 and T2
- we are trying to find the V1 (volume at STP) bc they have given us the mass (in grams) of the unknown compound, so if we have the volume we can find the density (g/L) of gas at STP
- it asks for MM –> g/mol
- multiply density (g/L) by the STP volume of 1 mol (22.4L/mol) to get MM (g/mol)
one mol of gas, no matter what type of gas will occupy
22.4 L/ mol at STP
gas held at a constant temp
P and V are inversely proportional
- one increase the other decrease
if temp increases and pressure is constant
volume increases
if n and V are constant, and temp increases
pressure increases
when 2 gases are in a container and they don’t chemically interact, how do they behave?
as if they don’t know the other one is in there
- the pressure that each gas exerts (the partial pressure) is the same if the gas is by itself or with another gas
- they act independently
the total pressure of the gaseous mixture
the sum of partial pressures
the partial pressure of a gas
is related to the mole fraction of each gas and the P total
Pa= Pt x mole fraction
mole fraction
moles of x/ total moles
Henery noticed that?
at different pressures the concentration of a gas in. a liquid changed
- the solubility of a gas will increase with increasing partial pressure of the gas
- if Pa increase—> [A] increases
Vapour pressure
the pressure exerted by evaporated particles above the surface of a liquid
solubility/ concentration and pressure
are directly related
Grahams law
gases with lower MM will diffuse or effuse faster than those with greater MM
Effusion vs Diffusion
- effusion - movement from one container to another through small opening
- diffusion- spreading out of particles in the same container
when do gases deviate from ideal gases
when variables (P,T,V) are changed in a way that brings them very close together
- High P
- Low V
- Low T –> bc there movement slows and their intermolecular forces become moe significant!
root-mean square speed
Urms= Square root of (3RT/MM)
- M in kg/mol
