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Chemistry Review 2

The first chemistry review brought back so many 10 year old memories that I decided to do it again, this time reliving the second semester of freshman chemistry.

The WKU spring semester started about a week and a half late because the Icestorm of 1994 (I believe it was an Alberta Clipper) had shut down the interstates in Kentucky and Tennessee. With an enrollment of approximately 17,000 at the time, most WKU students commuted; barely 3,000 students lived on campus, and many of those went home on the weekends, and thus WKU is called a "suitcase college." The ice storm hit the weekend before classes were to start, and as a result, classes were cancelled until local roads were safely passable. Regardless, many students still couldn't get to Bowling Green when classes did start.

It was so cold after the storm that the road salt couldn't melt the 4-6 inches of ice and the foot of snow coating it. Before the storm, the temperature was above freezing, then came the powerful cold front and the mercury plummetted overnight. The rain became freezing rain, which gave way to sleet. The sleet fell for several hours before turning to snow. After the front passed, the snow stopped, but the temperature was below 0 F for days, dipping below -20 F at night.

I remember three things from this month:

  • Misty's car totalled in a 4:30am car wreck. The other car ran a red light, hit her rear passenger wheel, and spun us around for what seemed liked forever. I think we spun around 1.5 times. This was a day or two before the icestorm.
  • While wooing Tiffany after the storm, bringing a pint of milk to her dorm room from the cafeteria.
  • People slipping and falling on the ice all over campus... and taking several falls, myself.
  • The cold prickliness of snot freezing in my nostrils.

On with the chemistry review! I've skipped the second half of thermodynamics and moved on to kinetics:

    Kinetics

  • Reaction Rate affected by: temperature, reactant concentration, nature of the reactants, and catalysts
  • reactantA + reactantB = product(s)
  • rate = k[a]^x [b]^y . . . k is the rate proportionality constant
  • order of the overall reaction is sum of all exponents; for a single species, use the exponent
  • k = (rate) / [a]^x [b]^y
  • Zero Order Reactions over time: [a]0 - [a]t = kt (duh)
  • First Order Reactions over time: ln ([a]0 / [a]t) = kt
  • Second Order Reactions over time: (1 / [a]t) - (1 / [a]0) = kt
  • First Order Half Life is independent of concentration: t(1/2) = (ln 2) / k
  • Second Order Half is dependent on initial concentration: t(1/2) = 1 / (k * InitialReactantConcentration)
    ...
    Activation Energies
  • Activiation Energy = Ea
  • Collision Theory: rate of reaction is dependent on reactants colliding with proper orientation and sufficient kinetic energy to have an effective collision
  • Transition State Theory: study of what happens when reactants collide; think activation energy diagrams, and you have the general idea
  • Transition State is the peak of the activation energy diagram when the activated complex is formed
  • Activated Complex has partially formed bonds; once formed, the reaction can product the product (or reverse back to the reactants - bummer)
  • High Ea: much bond breaking occurs
  • Low Ea: bond breaking and bond formation absorbing/releasing roughly equivalent amounts of energy
  • Arrhenius equation considers effect of temperature on reaction rate: k = A * e ^ (-Ea / RT) . . . A is frequency factor, R is gas constant [8.314 J / (mol * K)], T is kelvins
  • To find Ea: ln (k2 / k1) = (Ea [T2 - T1]) / (R * T2 * T1)
    ...
    Equilibrium
  • Dynamic Equilibrium is achieved when there is no net change in the concentration of reactants and products
  • Equilibrium Constant: Kc = [products]^x / [reactants]^y . . . concentration of products divided by concentration of reactants; each is raised to the power of its coefficient in the balanced chemical equation
  • Mass Action Expression: the [products]/[reactants] representation
  • Reaction Quotient: Q . . . the value of the mass action expression; when the reaction is at equilibrium, Q = Kc
  • For ammonia: N2 + 3(H2) --> 2(NH3): Kc = [NH3]^2 / [N2][H2]^3
  • Kc varies only with temperature; for a given temperature, the Kc for a reaction never changes; that is, no matter what concentrations of the reactants and products are added for reaction, the concentrations will adjust until Q = Kc
  • Higher Kc = more products, and vice versa; if lowering the temperature lowers Kc, then lower temperature shifts the equilibrium to favor the reactants
  • Very high Kc means the reaction more or less goes to completion to achieve equilibrium; example: 2(H2) + O2 --> 2(H2O) has Kc greater than 10^80!
  • To add equilbrium reactions, multiply the Kc values
  • You have a choice with gases: you can also use partial pressures, because it's proportional to molar concentration: from PV = nRT, P = [GasMolarity] * RT
  • If using molarity, you get Kc; if using partial pressures, you get Kp
  • To convert equilibrium constants molarity <--> partial pressure: Kp = Kc(RT)^(delta-moles-gas)
  • Kp = Kc if the number of moles of gas remains constant, for example, H2 + I2 <--> 2(HI)
  • Borrowing from the thermodynamics material skipped, G is Gibbs Free Energy; (delta-G) is the Gibbs Free Energy Change... if (delta-G) is negative, the reaction proceeds spontaneously, and vice versa; (delta-Go) is Gibbs Free Energy Change at standard temperature and pressure (25C, 1atm)
  • (delta-G) = (delta-Go) + RT ln(Q) . . . R = 8.314 J/(mol*K)
  • Thermodynamic Equilibrium Constant: (delta-Go) = -RT ln(K) . . . here, K is equilbrium constant (Kc or Kp) and not Kelvins

:: Bryan Travis :: 09/29/2003 @ 07:25 :: [link] ::
...


Wedding Music

Let's face it - grooms-to-be have a notorious stereotype of being useless wedding planners. I wish I were more enlightened and new agey, but alas, I fit the mold of the aloof and distant groom to a tee.

The wedding is two hours from where I live, though, and I'm in the vicinity every other weekend, and I'm having a hard time finding ways to be helpful. If you have any suggestions, please - email me now!

Meanwhile, Rachel has asked me to select music. A few selections I have in mind thus far... a bittersweet, often darkly humorous and eclectic selection sure to shock our guests (samples require RealPlayer):

:: Bryan Travis :: 09/28/2003 @ 13:03 :: [link] ::
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Glimpses of a Fantasy World

Yeah, yeah, yeah... don't you wish it were socially acceptable to rest your arm on the bare thigh of women and stare at their bosoms while they lustfully adored your receding hairline?

:: Bryan Travis :: 09/13/2003 @ 12:01 :: [link] ::
...

Seattle's Initiative 77

Next Tuesday Seattle residents vote on Initiative 77, an innocuously-named proposal to place a 10 cent tax on espresso-based drinks to fund childcare for low income parents. This would set a dangerous precedent by sending the message that it's okay to single out products for taxation.

I can appreciate the theory behind what they're trying to do: espresso drinks are luxury items consumed mostly by the upper middle class and upper class; Seattle intends to use sales of espresso as an indicator of wealth, and thus tax higher income individuals via their discretionary spending. But I disagree completely with the approach. In the interests of full disclosure, I am an espresso addict, but not a frequent coffeeshop patron because I usually brew my own lattes.

A flat sales taxes is one thing, but I oppose Initiative 77's concept because it seeks to tax a single product whose production and consumption does not affect the problem being addressed. For example, cigarettes and alcohol increase health care costs; owning property means you benefit from the services of the local fire department and public school system; burning gasoline and driving cars increases environmental impact and wears out roads... gasoline, cars, property, cigarettes, and alcohol are taxed because they increase costs government entities must absorb. Now, whether those tax revenues directly benefit the expenses they were imposed to fund is another question, but it works out at the level of total expenses verus total revenues.

In the case of Initiative 77, the production and consumption of espresso beverages is not related to low income families' need for childcare. Therefore, the government should not single out espresso and tax it. It just doesn't make sense.

As a liberal, I agree with the theory behind Initiative 77, that higher income individuals should carry more of the tax burden. And to an extent, I can appreciate with Jesse Ventura's opinion that people should be taxed according to the lifestyle they choose to live, not their incomes (that is, eliminate income tax and increase sales tax). My only concern is that individuals and especially corporations will find loopholes in sales tax laws. For example, today there are only state sales taxes, which don't apply if the buyer and seller make the purchase from different states (that is, via mail order, purchase order, or online), but do apply if both buyer and point-of-sale are in the same state - such policies favor corporations over individuals. If there were a national sales tax, what taxation would occur if buyer and seller were in the U.S. and another country? I suppose an extensive taxation policy such as the European VAT tax (which I believe the buyer pays even through mail-order and online purchases) would close most loopholes.

But let's not fool ourselves: sales tax has a high transactional frequency - it occurs whenever a purchase is made, and is easily noticed. Income tax withholdings are more transparent on a paycheck, and have their highest visibility that one time a year when filling out tax forms. There seems to be an impulsive, irrational trait of American culture: if given the choice between no income tax with a high sales tax on every purchase, and no sales tax with a high income tax paid annually, I think they'd opt for the income tax, even if the sales tax plan resulted in less taxes paid per individual. What really matters from a financial perspective is the bottom line - how much does it cost? But as a culture, we focus on the wrong quantitative variable - we focus more on number of transactions than the total expense to our pocketbook. That just doesn't make sense, either, but that's another issue altogether.

:: Bryan Travis :: 09/13/2003 @ 11:48 :: [link] ::
...


Chemistry Review 1

One- and two-liners heard recently:

  • If you don't think too good, don't think too much.
  • There's nothing right in my left brain, and nothing left in my right brain.

So, dudes, I've started going through my biology and chemistry notes from my college undergrad days. It's constant deja vu. I can't recall much of it off the top of my head or when looking over review questions, but like learning a new language or walking down a long forgotten path, going through my notes is like deja vu... oh wait, I've already said that.

Currently I'm reliving freshman chemistry. A brief introduction:

My first semester of freshman chemistry was a near-disaster, which taught me several valuable lessons. The class was at 8:00am on Tuesday, Thursday and every other Friday, but I am not a morning person - not even close. Nevermind the fact that I made it to elementary and high school everyday by this time - I was on my own and didn't have parents to make sure I woke up everyday. Either the professor wasn't very organized, or his teaching style wasn't compatible with my learning style... combined with the 8:00am class schedule, it was too much, so I skipped most classes from the last week of September through the first week of November, electing instead to have an 8:00am breakfast with a friend in the class who also skipped out.

I couldn't understand anything the professor was talking about after going back to class the first week of November. As finals loomed nearer, I began to realize how terribly screwed I was. In the first two weeks of December as I struggled to catch up for the final, I drank so much coffee on the weekends that my hands had a constant tremor. Get this - I broke out in hives that itched and swelled in the cold air outside because the anxiety was so intense. It's probably the closest I've ever come to a nervous breakdown.

Somehow I scored in the mid 70s on the final and emerged from the class with a B. First lesson learned: never register for an 8am class unless nothing else was available (there were only two 8am classes in my entire college career). Second lesson learned: no matter how bad the professor or how hard to get out of bed, never skip more than 2 or 3 classes in a course.

I took the second semester of chemistry with another professor whose teaching style was very organized, conducive to my learning style, or both. Reading the second semester notes, I can actually remember the thoughts going through my head whenever the professor explained something the other professor bumbled over or that I had missed out on entirely. It was like a weight lifted, a revitalizing breath of pure oxygen when climbing a high mountain, the sun peeking through overcast clouds. A 10:30am course, I never missed a lecture, got an A, and managed to recover the first semester material during reviews for the freshman year chemistry comprehensive final exam.

  • Gassy Stuff
  • Graham's Law, or Law of Effusion: effusion rate -> 1 / (SqRt-density)
  • ...
  • Solutions
  • % solute = (weight of solute) / (weight of solute + solvent)
  • M (molarity) = (moles solute) / (liters solution)
  • mole fraction = (moles compound) / (total moles in solution or mixture)
  • m (molality, less common and not to be confused with molarity) = (moles solute) / (kg solvent); fortunately, in dilute water solutions, m and M are more or less equivalent, so chill
  • ..
  • Colligative Properties depend more on concentrations of mixtures than chemical identity of the solute(s) and solvent. Examples are lowering vapor pressure and freezing point, raising boiling point, and osmotic pressure. For example, 0.10M solutions of urea and sucrose in water have the same effect on water's colligative properties (same boiling/freezing points, water vapor pressure, etc).
  • Ideal Solution Law / Raoult's Law: (P1 = X1 * Pa1); in other words, an 80% mole fraction of the solvent in the solution means the solvent's vapor pressure is 80% of the pure solvent's vapor pressure.
  • Freezing point depression: (Delta Tf) = (m * Kf * i) ... Kf is the freezing point depression constant, which differs by solvent; i is van't Hoff factor
  • Boiling point elevation: (Delta Tb) = (m * Kb * i) ... Kf is the boiling point elevation constant, and differs by solvent; i is van't Hoff factor
  • van't Hoff factor: i = (# particles in solution) / (particles first added)... when CaCl2 is dissolved in solution, each molecule disassociates into 3 particles, so CaCl2 i = 3, and NaCl i = 2. Well, this isn't exact... as the concentration of the solute increases, so does i; thus, a 0.1M NaCl solution actually has a factor of 1.87.
  • Ideal Gas or van't Hoff equation: PV=nRT ... actually, use pi instead of P for solutions... Pi = osmotic pressure; V = liter volume; n = number mol; R = ideal gas constant (0.0821 L-atm/mol-K); T = kelvins
  • Cool Factor: at 0.01 Celsius and 0.006 atmospheric pressure, water is a gas, liquid, and solid at the same time! And below 0.006 atmosphers, water is never liquid - it goes between vapor and solid states.
  • ...
  • Acids and Bases
  • Arrhenius says: acids form H30+ in water; bases form OH- in water... but the only solvent in his chemistry set was water, so it isn't the commonly accepted defintion today, okay, fool!
  • Strong hydroxide-forming (OH-) bases containg I-A and II-A metals. Sweet!!!
  • Bronsted-Lowry says: acids donate protons; bases accept protons... these dudes didn't use just water in their chemistry sets, but this definition isn't perfect in all cases...
  • Lewis says: I'm gonna one-up you three bastards and expand the realm of acids and bases even further! What if there isn't a solvent or even a proton to kick around? Acids are electron pair acceptors; bases are electron pair donors! Therefore, acids include molecules whose central atom has an incomplete electron octet, simple cations such as Fe 3+ and Ag+, and compounds which can expand their octet (only elements higher than neon do this). And bases now include all ligands, which are negative ions, but also neutral atoms with a free electron pair, such as ammonia and even water! Take that, bee-atch!
  • ...
  • Thermodynamics
  • E = KE + PE . . . Total Energy = Kinetic Energy + Potential Energy
  • delta E = Efinal - Einitial = Eproducts - Ereactants . . . energy
  • delta T = Tfinal - Tinitial . . . temperature
  • delta H = Hfinal - Hinitial . . . enthalpy
  • delta S = Sfinal - Sinitial . . . entropy
  • delta G = Gfinal - Ginitial . . . Gibb's free energy
  • Heat Capacity * (delta T) = heat energy
  • Specific Heat = heat capacity / gram ... units J/(g-C)
  • Heat Capacity = (Specific Heat) * Mass
  • Molar Heat Capacity is heat capacity per mole ... units J/(mol-C)
  • Enthalpy is total energy of a system at a constant pressure (H), and changes in enthalpy can occur as work (w) or heat (q)
  • (delta H) = (delta E) + P * (delta V)
  • Endothermic: (delta H) is positive - system gains heat
  • Exothermic: (delta H) is negative - system loses heat, FOOL!
  • If all heat of reaction (delta H) is released as heat - that is, no work is done by the system, then (delta H) = q, at a constant pressure
  • Standard heat of reaction = (delta Ho) in kJ, using however many moles are specified by the coefficient of the chemical reaction
  • Hess' Law: whether you calculate (delta Ho) for a reaction directly or by summing heats of formation (delta Hof) through intermediate steps to reach the final product(s), (delta Ho) is always the same, because energy cannot be created or destroyed, okay, FOOL!
  • (delta G) = (delta H) - T * (delta S)
  • + (delta H) and + (delta S): reaction spontaneous at high T
  • + (delta H) and - (delta S): reaction not spontaneous at all T
  • - (delta H) and + (delta S): reaction spontaneous at all T
  • - (delta H) and - (delta S): reaction spontaneous at low T
  • Equilibrium: Gproducts = Greactants and (delta G) = 0
  • Equilibrium Temperature: T = (delta H) / (delta S)

:: Bryan Travis :: 09/06/2003 @ 20:08 :: [link] ::
...