Thermodynamics

- Enthalpy (∆H) AND Entropy(∆S) are state functions (only numbers that matter are beginning and end)

- Enthalpy: measure of the TOTAL ENERGY of the system (joules)

Bond Formed = -∆H (energy released)

Bond BROKEN = +∆H (energy absorbed)

- Hess’s Law: summation of enthalpies

- Spontaneity depends on ∆G (∆G = ∆H - T∆S) graphable

∆G will tell you whether a reactions happens or not!

…will tell you NOTHING about rxn rate.

∆G / spontaneity is dependent on temperature, NOT necessarily on ∆H and ∆S.

NEG ∆G = spontaneous

POS ∆G = non spontaneous

ZERO ∆G = equilibrium

∆Gf indicates whether we have a stable or unstable compound relative to its elements.

NEG ∆Gf = STABLE… will spontaneously form compound.

POS ∆Gf = UNSTABLE… will not spon. form compound, need to input energy into the system

POS ∆S = increase in disorder

NEG ∆S = decrease in disorder

Consider why according to eq:

ex: ATP-coupled reactions

ex2: Hydrogen bonding

Apr 09, 2011

Which of the following best describes enthalpy?

(a) Energy that is not available for work in a thermodynamic system (Entropy)
(b) Energy stored in a system derived from its configuration (PE)
(c) The energy of motion in an object (KE)
(d) The total energy of a thermodynamic process (Enthalpy)

uh oh...

So my progress with my MCAT studying this summer is starting to suffer courtesy of road trips and football preoccupations... but all it takes is a few clicks around the internet and a cursory glance at my progress report to briskly scoot my little ass to the kitchen table to forge forward! Viva la estudia!

Rates of Reaction

Learn to always consider reactions in terms of a "decrease in reactants"or an "increase in products" obviously with respect to concentration and the presence of catalysts... helps to think of rate laws and rate-determining steps faster.

5 factors that affect rate: 1) concentration of reactants, 2) temperature, 3) presence of catalyst, 4) rxn medium, 5) surface area of reactants
Observing rate change from physical properties:
(1) COLOR -- measure change in absorption of electromagnetic radiation
(2) Change in PRESSURE w/ gases -- change in number of gaseous molecules

Reaction: aA + bB →(C)→ dD + eE

Rate Law = k [A]^m [B]ⁿ [C]^p

*** DO NOT WRITE THE CO-EFFICIENT for the exponents… they are EXPERIMENTALLY DETERMINED and must be derived from calcuculating the rate order from a table of trials!!!

Caluclating Rate Order:
1. Find trials in which target conc. [A] changes and other conc. variables [B] and [C] stay the same.
2. Note how the rate changes for those 2 trials, and deduce order from rate change:

Rxn order (m):	Rate mult. by:
-1	½
0	1
1	2
2	4

3. Solve for k by plugging in data from ONE trial into the "rate law equation"
Arrhenius Equation: dependence of reaction rate on TEMPERATURE.

k = A e^{-Ea / RT}

A Gassy Matter

Perhaps the most important characteristic of our gas friends is their compressibility--their ability to be squeezed into a smaller volume by the application of pressure. Anyone snorting O2 from steel cylinders can appreciate this.

The most important conditions of gases are volume, pressure, temperature, and molar amount. You can understand that the nature of a gas heavily depends upon the conditions under which it exists.

V & P (INVERSELY proportional). When pressure is doubled, the volume is halved. (Boyle's Law).
x2 P, 1/2 V
x2 V, 1/2 P

V & T (DIRECTLY proportional), why a gas contracts when cooled and expands when heated, ex: hot-air balloon (Charles' Law).

GAS LAW PROBELMS MUST ALWAYS BE DONE WITH TEMPERATURE ON THE KELVIN SCALE!!!!!!!!!! +273

Avogadro: two gases under the same atmospheric condition, STP, must have the same number of moles of gas (n).

“It is assumed that molecules in an IDEAL GAS have NO VOLUME and that there are NO INTERACTIONS between the molecules.”

From all this we derive the ideal gas law, the king shiz of all gas laws, PV = nRT.

exam:

P of gas increases when "n" number of molecules increases

- meaning # of molecules increases

- to find # of molecules of a gas in 25 gram sample, divide the "molar mass of the gas" into 25 g...

1 mol gas = 22.4 L (volume of space!)

What about the density of a gas? Don't forget that D = m/v. Since density depends on volume and the volume of a gas varies with temperature and pressure, the density of gas ALSO varies with temperature and pressure.

Of note: Density of a gas is directly proportional to its molecular weight. Bromine is 5x heavier than oxygen. Bromine gas (a reddish brown stink-o-maticks) is 5x denser than oxygen!!

Dalton, being the partial guy that he is, went on to say that the pressure exerted by a gas is the sum of all its partial pressures. (P = P1 + P2 + P3...)

The Kinetic-Molecular Theory: gas pressure is the result of the bombardment of the container walls by constantly moving molecules.
- PRESSURE all depends on the NUMBER of gas molecules in a container, related to how FAST they're moving (frequency of collisions).
- Altering the volume or temperature of a gas in a container will invariably alter its pressure and therefore, kinetics.

Effusion
Graham's Law: rate of effusion is inversely proportional to the square root of the molecular weight... wah?
- the heavier the gas, the slower it will diffuse! (think of how slowly the fat kid diffuses through la cancha on field day...)

r_a x M_a^½ = r_b x M_b^½

^{rate of 2 gases effusing together: (M_b/M_a)½}

Rate is always expressed as (1/unit time)!

Buildings Blocks

Amino Acids - PROTEINS
Nucleotides - NUCLEIC ACIDS
Fatty Acids - FATS/LIPIDS/MEMBRANES
Sugars - POLYSACCHARIDES

condensation - expels water, "condenses" monomers
hydrolysis - consumes water, decomposes polymers