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# THE MCAT-CHEM 8

### PHASE AND PHASE EQUILIBRIA

Formula relating pressure, force, area P = F / A -F = weight of mercury that got pushed up -A = cross-section area of column
1 atm = _______ mmHg = _______ torr = ______ kPa 760 / 760 / 101
What does it mean for a pressure to be 760 mmHg? 1 atm of pressure will push mercury up by 760 mm
P = F/A results in what units? pascals
ideal gases occupy how many liters per mol of molecules? 22.4 L
Ideal gas theory -random molecular motion -no IMF -no molecular volume -perfectly elastic collisions
Ideal gases are best at __ pressures and ___ temperatures low / high
ideal gas law PV = nRT
At high pressure and low temperature, what happens to gas molecules? condense into liquids
Boyle's Law pressure and volume are inversely proportional
Charle's Law volume and temperature are directly proportional
Avogadro's Law Under STP, equal volumes of gases have equal number of molecules (number of molecules calculated from volume)
What is temperature a measure of? average KE of gas molecules
Effusion random molecular motion to cause a substance to escape through a very small opening
Graham's Law Rate1 / Rate2 = square root (M2 / M1)
2 gases diffuse down a tube from opposite ends, where will gases meet? lighter gas will travel faster
T / F: At a given temperature, all gases have the same KE TRUE
What is Graham's Law derived from Kinetic energy
"b" term in Van der Waal's -bounce --> repulsion term -greater b, more repulsion, greater pressure, greater volume
"a" term in Van der Waal's -attraction -greater a, more attraction, less pressure, smaller volume
Dalton's Law for Partial Pressure Pi = xi * P(total)
What are the most common hydrogen bond acceptors? F / O / N
Hydrogen bonding _____ boiling point. increases
The stronger the hydrogen bond, the more / less polar a bond is. more polar
Rank polarity for HF, HN, HO HF > HO > HN
Dipole-dipole interactions polar molecules align so that opposites attract
Do dipole-dipole interactions increase BP as much as H-bonding? NO
Stronger dipole interactions, more / less polar molecule is. more
Why are ion-dipole interactions stronger than dipole-dipole interactions? interaction between a full charge (ion) and a partial charge (dipole)
For polar molecules, which forces are predominant? For non-polar? dipole / dispersion forces
What creates dispersion forces? induced and instantaneous dipoles
induced dipole polar molecule interacts with a nonpolar molecule and induces a dipole in nonpolar
instantaneous dipole nonpolar molecules have randomly fluctuating dipoles
Dispersion forces get stronger for smaller / larger molecules? larger
Do liquids experience IMF? YES
Can you compress a liquid? A gas? mostly no / yes
Triple point Temp. and pressure at which s,l,g all coexist in equilibrium
critical point Temp. and pressure at which liquids and gases become indistinguishable
critical temperature temperature above which you can no longer get gas-> liquid no matter how much pressure applied
How is the water phase diagram different from others? solid / liquid boundary is slanted to left -water is more dense than ice
Freezing point is the same as ________ and are found in the _____ phase boundary. melting point / solid - liquid
Boiling point is the same as ___ and are found in the ____ phase boundary. condensation point / liquid - gas
sublimation conversion of solid to gas
molality vs. molarity -molality = (mol solute / kg solvent) -molarity (mol solute / L solution)
colligative properties properties that depend on number of solute particles but not on type
Solute particles (increase / decrease) vapor pressure, BP, FP? decrease, increase, decrease
Boiling point elevation eqn delta Tb = Kb * m * i
Freezing point / melting point dpn eqn. delta Tf = -Kf * m * i
osmotic pressure n = MRTi -n = osmotic pressure
What is osmosis? mvmt of solvent from low solute --> high solute concentration -solvent will move from area with low n to area with high n
Relation btwn osmosis and osmotic pressure osmotic pressure determines what direction osmosis will occur --solvent will move from area with low n to area with high n
If you have 100 particles of CaCl2 but 30 dissociate, what is i factor? -30 Ca + 60 Cl + 70 CaCl2 -160 / 110 = 1.6
solution mixed at molecular level and will always stay mixed
colloids and example mixed at semi-molecular level that tiny solute aggregates -fog, milk, water + oil
suspension things that are mixed at particle level and will NOT stay mixed
Henry's Law and eqn -amt of gas that dissolves in a given type and volume of liquid is directly proportional to the partial pressure of that gas in equil with that liquid -Partial pressure of solute = k * [solute]
Vapor Pressure eqn Vapor pressure = X(solvent) * Vapor pressure of pure solvent alone X(solvent) = mols of solvent / total mols of both solute and solvent
What does a b-value describe for a gas? -size --> greater MW gases have greater b-values
Where is the greatest a-value found for a gas? strongest IMF
Gas that is closest to an ideal gas has ___ a-value and b-value. small
A lighter gas has more / less collision momentum & impulse. less
T / F; At the same temperature and conditions, all gases have different average KE. FALSE --> all gases have the same average KE
Relative speeds of gases under identical conditions depends on _____. masses
Evacuating a container allows fewer collisions and allows the gas to travel at (faster / slower) speeds? faster
For a balloon to float in the air, what 2 forces must be equal? buoyant force and weight
Does a buoyant force depend on contents of a balloon? NO --> depends on density of surrounding medium and volume of object
Conjugation allows a species to absorb / reflect light? absorb
Do atoms vary in size during molecular packing and bonding? NO
How do electrons travel through an electrical conductor? delocalized molecular orbitals (conjugated pi bonds)
How many bonds does P make? 3
What is boiling point? point at which VP = P(atm)
More / less ions in solution results in better conductivity. more
Which phase change absorbs the greatest amount of energy? sublimation
For a cpd to be liquid at room temp, BP must be _____ than room temp and MP must be ___ than room temp. greater (otherwise would be a gas) less (otherwise would still be a solid)
positive deviations from an ideal gas are due to? negative deviations from an ideal gas are due to? -"b" term for molecular volume -"a" term for attraction
A real gas exerts more / less pressure than an ideal gas? less
Volume deviates positively / negatively from ideal behavior and pressure deviates positively / negatively? positively / negatively
calculate KE for a gas. KE = 3/2 RT
What is difference btwn kinetics and thermodynamics? -kinetics deals with rate of rxn as it moves towards equilibrium -thermo deals with balance of R and P after reaching equilibrium
What does increasing the T do for a rxn and its equilibrium? equilibrium is achieved more quickly
Does temperature affect the activation energy? NO
What factors affect the rate of a rxn? Temp, pressure, concentration of certain substances
Catalyst substance that increases rxn rate without being consumed or altered by lowering Ea
Do catalysts increase the forward or reverse rxn? BOTH
What is a biological catalyst? enzyme
heterogenous catalyst vs. homogenous catalyst -heterogenous catalyst = different phase than R or P -homogenous catalyst = same phase as R or P
Do liquid or gas molecules make more collisions? liquid --> a lot closer to each other
Do collisions in a liquid occur faster or slower than collisions in a gas? about the same rate
A constant rxn rate characterizes a _____ order rxn zero
What do real gases have? IMF and particles with real volume
How do impurities in organic solids affect MP of solid? lowers MP and broadens temp. of melting
Freezing and melting point _______ Boiling point ______ depression / elevation
In a gas system with 2 flasks connected together, does the mole fraction change? does the number of moles change? NO / YES
How does rate of diffusion change with time? decreases for all gases
What is molecular mass? mass per moles
Do number of moles change with temperature or pressure? NO
To float a balloon, should it be in a less dense or more dense medium? more dense
The velocity of a gas particle depends on? mass and its temperature
Formulas for KE of gases? KE = 1/2 mv^2 KE = 3/2 RT
In a manometer, what is the force pulling the mercury down? What is the force pulling the mercury up? -down = F = mg -up = F = PA
Infusion vs. Effusion -Effusion = gas escaping from container to env't through pores -Infusion = gas entering container from env't
How is diffusion different from effusion and infusion? Diffusion does not involve gas passing thorugh pores
Generally, gas particles that can pass through pores have the fastest? velocity
For results that yield small changes, should a more dense or less dense liquid be used for measurement? less dense
What is the role of the stopcock? equilibrate the pressure of the two sides of the manometer before the reaction begins
Why is mercury used for manometers? density prevents spillover
When is water densest? 4C
Is ice more or less dense than water? less dense
When water starts to freeze and solidify at 4C, what happens to its volume? volume increases
Created by: 507935299