Phases and Gases Flashcards
vapor pressure
- the force exerted by the gas particles that vaporize from a solid or liquid sample
vapor pressure depends on
- the substance itself only
- not external pressure
- proportional to temperature and KE
- indirectly proportional to IMF
boiling point
- the temperature at which the condensation/vaporization phase transitions occur
- when Pvap=Patm
boiling point depends on
- external pressure directly proportional
- intermolecular forces directly proportional
boiling point elevation
- dissolve a solute in a solvent, the additional IMF add more bonds that must be broken to achieve boiling
factors affecting boiling point
- IMF (inc IMF inc BP dec Pvap)
- Molecular weight (inc MW inc BP)
- branching (dec branching inc BP)
melting/freezing point
- the temperature at which the fusion/crystallization phase transitions occur
- same rules as melting point
FP depression
- dissolve a salt in water, the ions act like a road block to water arranging in a regular crystal lattice
- so, it must get even colder before things will freeze with ions in the way
solute
- present in a small quantity
solvent
- present in a larger quantity
- usually water on the MCAT
strong electrolyte
- complete dissociation
weak electrolyte
- partial dissociation
non-electrolyte
- no dissociation
van’t hoff factor
- the number of particles produced in solution per mole of substance
- number of particles it breaks down into when it dissolves
electrolytes dissolve in water
- agitation (endothermic) - breaking bonds
- dissociation (endothermic) - breaking bonds
- solvation (exothermic) - forming bonds IMF
polar non-electrolytes dissolve in water
- agitation (endothermic)
- solvation (exothermic)
nonpolar non-electrolytes do not dissolve in water
- agitation (endothermic)
- won’t dissolve.
solubility
- the amount of a substance that can dissolve in a specific solvent AT A SPECIFIC TEMPERATURE
unsaturated solution
- concentration of solute < solubility
- additional solute can still dissolve
saturation solution
- concentration of solute = solubility
- no additional solute will dissolve
supersaturated solution
- concentration of solute > solubility
- additional solute causes excess to precipitate
solids and liquids in water
- solubility directly proportional to temperature
- not affected by pressure
gaseous solutes in water
- solubility indirectly proportional to temperature
- directly proportional to pressure
always soluble
- group 1 ions
- H+
- NH4+
- NO3-
- CH3COO- (acetate)
- ClO4-
usually insoluble
- Ag+
- Pb2+
- Pb4+
- Hg2 2+
- Hg2+
- Co3 2-
- PO4 3-
- S2-
strength of IMFs
- solids > liquids > gases > ideal gases
liquid to gas
- vaporization (boiling)
gas to liquid
- condensation
solid to liquid
- fusion (melting)
liquid to solid
- crystallization (freezing)
solid to gas
high imf to low imf
- sublimination
- heat absorbed
- internal KE increases
- entropy increases
- dec IMF
gas to solid
low imf to high imf
- deposition
- heat released
- Internal KE decreases
- entropy decreases
- inc IMF
boundary line between two phases
- all the T/P points at which the two phases exist in equilibrium
triple point
- the one T&P when all three phases coexist in equilibrium
critical point
- the T&P above which the different between liquid and gas is no longer distinct
- properties of both liquid and gas
phase diagram of water
- same general trend of other phase diagrams except negative slope at solid-liquid boundary
- freezing point/melting point of ice decreases under increasing pressure (how we are able to ice skate)
density
- measure of how condensed a substance is
- p=m/V
density affected by
- external pressure directly proportional to density
- external temperature indirectly proportional to density
- IMF directly proportional to density
formulas for heat
q=mcΔT (for temperature change)
q=nΔH_phase change (for phase change)
CANNOT HAPPEN AT THE SAME TIME!
inverse of slope on heating curve
- equals c
- smaller slope = higher heat capacity
potential energy and IMF
- PE increases as IMFs break
ideal gas
- has no IMFs
- particles with negligible volume compared to their container size
- an average KE proportional to its temperature
- elastic collisions between particles and container walls (creates pressure)
- favored with high temperature and low pressure since interactions of the particles are minimized
ideal gas law
PV=nRT
R=0.08
V=22.4L at or near 1 atm, 273K
units for pressure
- 1 atm = 101 kPa = 760 torr = 760 mm Hg
units for volume
- 1L = 1000 mL = 1000 cm^3 = 0.001 m^3
units for temperature
- must be absolute temperature scale or kelvin
- C + 273=K
Avagadro’s law
- V=n
- V is proportional to n at a given P and T regardless of the identity of the gas
PlATe - Avo at P and T
Boyle’s law
- P = 1/V
- P1V1=P2V2
BAT - Boyle at T and n
Charle’s law
- T = V
- V1/T1=V2/T2
- CAP - Charles at Pressure and n
Gay-Lussac’s Law
- P = T
- P1/T1=P2/T2
combined gas law
- P1V1/T1 = P2V2/T2
- number of moles are still constant
- temp must be in K
non- ideality
- P_ideal > P_real
- V_ideal > V_real
- because the particles of a real gas DO experience IMF, their paths are deviated and thus the frequency of collisions on the container wall will result in a lower pressure
- because particles of a real gas DO have physical size, they take up space in the container and thus the free space in the container is smaller
Real Gas Law
(P + an^2/V^2)(V-nb) = nRT
- a increases as IMFs of a gas get stronger
- b increases as the size of a gas particle increases
Dalton’s law
- P_total = Pa+Pb+Pc……Pn
- the total pressure of a mixture of gases is equal to the sum of their partial pressures
mole fraction
- Pa=XaP_total where Xa=na/n_total
grahams law of diffusion/effusion
rate of gas 1 = sqrt (molar mass of gas 1)
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rate of gas 2 (molar mass of gas 2)
- heavy particles move slowly
- light particles move quickly
formula for density
p=m/v
STP
- 0 degrees Celsius
- 1 ATM
standard state
- 25 degrees Celsius
- 1 ATM.
mantra for ideal versus real
- ideal world is always greater than the real world.
