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THE MCAT-CHEM 8
PHASE AND PHASE EQUILIBRIA
| Question | Answer |
|---|---|
| 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 |
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