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}