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General Chemistry Ch. 8 - The Gas Phase
MCAT
18
Chemistry
Undergraduate 1
05/23/2016

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Term
What are the units used to express gas pressures? How do you convert between them?
Definition
1 atm (atmosphere) = 760 mmHg = 760 torr
Term
What is standard temperature and pressure (STP)?
Definition
273 K (0 C) and 1 atm
Term
What are standard state conditions?
Definition
298 K (25 C), 1 atm and 1 M concentrations
Term
How much volume does one mole of an ideal gas occupy at STP?
Definition
22.4 L, this is the same for all gases
Term
ideal gas law
Definition

PV = nRT

P is pressure (atm)

V is volume (L)

n is numer of moles

T is temperature (K)

R is the ideal gas constant = 8.21 x 10-2 (L•atm)/(mol•K)

Term
What is an ideal gas?
Definition
A hypothetical gas with molecules that have no intermolecular forces and occupy no volume; real gases deviate from this ideal at high pressures(low volumes) and low temperatures
Term
How is density incorporated into the ideal gas law?
Definition

PV = nRT

where n = m (mass)/M (molar mass)

Therefore, PV = mRT/M

and ρ = m/V = PM/RT

 

Term
combined gas law
Definition
P1V1/T1 = P2V2/T2
Term
Avogadro's principle
Definition

n/V = K or n1/V1 = n2/V2

all gases at a constant temperature and pressure occupy volumes that are directly proportional to the number of moles of gas present; as teh number of moles of gas increases the volume increases in direct proportion

Term
Boyle's law
Definition

for a given gaseous sample held at constant temperature (isothermal conditions), the volume of the gas is inversely proportional to its pressure

PV = k or P1V1 = P2V2

Term
Charle's Law
Definition

at constant pressure, the volume of a gas is proportional to its absolute temperature, in kelvins

V/T = k or V1/T1 = V2/T2

Term
Gay-Lussac's Law
Definition

constant volume, pressure and temperature are proportional

P/T = k or P1/T1 = P2/T2

Term
Dalton's law of partial pressures
Definition
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
Term
How to determine partial pressure of a gas
Definition

PA = XAPT

where XA= moles of gas A/total moles of gas

Term
Henry's law
Definition

the amount of gas dissolved in solution is directly proportional to the partial pressure of that gas at the surface of a solution

[A]1/P1 = [A]2/P2 = kH

[A] is the concentration of A in solution

P is the partial pressuer of A

kH is Henry's constant which depends on the identity of the gas

Term
kinetic molecular theory
Definition
  • 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 the walls are elastic
  • the average kinetic energy of the gas particles is directly proportional to temperature
Term
Graham's law
Definition

gases with lower molar masses will diffuse or effuse faster than gases with higher molar masses at the same temperature

v = √(T/mw)

Term
How do real gases deviate from ideal behavior?
Definition
  • at mdoerately high pressures, low volumes or low temperatures, real gases will occupy less volume than predicted by the ideal gas law because the particles have intermolecular attractions
  • at extremely high pressures, low volumes, or low temperatures, real gases will occupy more volume than predicted by the ideal gas law because they particles occupy physical space
  • the van der Waals equation of state is used to correct teh ideal gas law for intermolecular attractions and molecular volume
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