Ch 8 - The Gas Phase Flashcards
How does the density of gases compare to the other phases?
gases are the least dense phase of matter
What are the characteristics of gases?
- they are fluids and therefore conform to the shapes of their containers
- easily compressible
Which variables describe the gas systems?
- temperature (T)
- pressure (P)
- volume (V)
- number of moles (n)
What is 1 atm equivalent to for pressure?
1 atm = 760 mmHg = 760 torr = 101.325 kPa
What does a simple mercury barometer measure?
- incident (usually atmospheric) pressure
- as pressure increases, more mercury is forced into the column, increasing its height
- as pressure decreases, mercury flows out of the column under its own weight, decreasing its height
What is the difference between STP and standard state?
- STP: 273 K (0 C) and 1 atm
- standard: 298 K (25 C), 1 atm, 1 M
What is unique of ideal gases?
- ideal gases have no attractive forces between molecules
- though mass and volume are negligible, they are measurable
How much volume does 1 mole of an ideal gas occupy at STP?
- 22.4 L
- regardless of the identity of the gas, equimolar amounts of 2 gases will occupy the same volume and same temperature
What is the ideal gas law?
describes the relationship between the 4 variables of the gas state for an ideal gas
PV = nRT
What is Avogaadro’s principle?
- a special case of the ideal gas law for which the pressure and temperature are held constant
- it shows a direct relationship between the number of moles of gas and volume
n/V = k or n/V = n/V
What is Boyle’s law?
- a special case of the ideal gas law for which temperature an number of moles are held constant
- it shows an inverse relationship between temperature and volume
PV = k or PV = PV
What is Charle’s law?
- a special case of ideal gas law for which pressure and number of moles are held constant
- shows a direct relationship between temperature and volume
V/T = k or V/T = V/T
What is Gay-Lussac’s law?
- a special case of the ideal gas law for which volume and number of moles are held constant
- shows a direct relationship between temperature and pressure
P/T = k or P/T = P/T
What is the combined gas law?
- a combination of Boyle, Charles, and Gay-Lussac’s laws
- shows an inverse relationship between pressure and volume along with direct relationship between pressure and volume with temperature
PV/T = PV/T
What is Dalton’s law of partial pressures?
- states that individual gas components of a mixture of gases will exert individual pressures in proportion to their mole fractions
- the total pressure of a mixture of gases is equal to the sum of the partial pressures of the component gases
Pt = Pa + Pb + Pc…
Pa = XaPt –> Xa = moles of A/total gas moles
What is Henry’s law?
states that the amount of gas dissolved in solution is directly proportional to the partial pressure of that gas at the surface of a solution
[A] = kh x Pa or [A]/P = [A]/P = kh
What is the kinetic molecular theory?
attempts to explain the behavior of gas particles
- it makes a number of assumptions about the gas particles
What assumptions does the kinetic molecular theory make?
- gas particles have negligible volume
- gas particles do not have intermolecular attractions or repulsions
- gas particles undergo random collisions with each other and the walls of the container
- collisions between gas particles (and with the walls of the container) are elastic
- the average kinetic energy of the gas particles is directly proportional to temperature
What is Graham’s law?
describes the behavior of gas diffusion and effusion, stating that gases with lower molar masses will diffuse or effuse faster than gases with higher molar masses at the same temperature
r1/r2 = square root (M2/M1)
What is the difference between effusion and diffusion?
- diffusion: the spreading out of particles from high to low concentration
- effusion: the movement of gas from one compartment to another through a small opening under pressure
What are real gasses deviated from?
ideal behavior under high pressure (low volume) and low temperature conditions
What do real gases do at moderately high pressures, low volumes, or low tempeartures?
occupy less volume than predicted by the ideal gas law because they particles have intermolecular attractions
What do real gases do at extremely high pressures, low volumes, or low temperatures?
occupy more volume than predicted by the ideal gas law because the particles occupy physical space
What is van der Waals equation used for?
to correct the ideal gas law for intermolecular attractions (a) and molecular volume (b)
(P + n^2a/V^2)(V - nb) = nRT
- if a and b are both 0, the equation reduces to the ideal gas law
- a = attractive forces
- bb = ig particles
