Enthalpy Calculations (ΔH°f)

Key Concepts for Doing Enthalpy Calculations

1. When a reaction is reversed, the magnitude of ΔH stays the same, but the sign changes.
2. When the balanced equation for a reaction is mulitplied by an integer, the corresponding value of ΔH must be multiplied by that integer as well.
3. The change in enthalpy for a reaction can be calculated from the enthalpies of formation of the reactants and the products
4. Elements in their standard states are not included in the enthalpy calculations for the reaction since the enthalpy of an element in its standard state is zero.

ΔH° = Σ(ν × ΔH_f°) (products) - Σ(ν × ΔH_f°) (reactants)

-- ΔH = exothermic

+ ΔH = endothermic

Hund's Rule (Quantum Numbers)

name	symbol	orbital meaning	range of values	value example
principal quantum number	n	shell	1 ≤ n	n = 1, 2, 3, …
azimuthal quantum number (angular momentum)	ℓ	subshell (s orbital is listed as 0, p orbital as 1 etc.)	0 ≤ ℓ ≤ n − 1	for n = 3: ℓ = 0, 1, 2 (s, p, d)
magnetic quantum number, (projection of angular momentum)	mℓ	energy shift (orientation of the subshell's shape)	−ℓ ≤ mℓ ≤ ℓ	for ℓ = 2: mℓ = −2, −1, 0, 1, 2
spin projection quantum number	ms	spin of the electron (−½ = counter-clockwise, ½ = clockwise)	−½, ½	for an electron, either: −½, ½

This model describes electrons using four quantum numbers, n, ℓ, m_ℓ, m_s. It is also the common nomenclature in the classical description of nuclear particle states (e.g. protons and neutrons).

• The first, n, describes the electron shell, or energy level.
  • The value of n ranges from 1 to "n", where "n" is the shell containing the outermost electron of that atom. For example, in caesium (Cs), the outermost valence electron is in the shell with energy level 6, so an electron in caesium can have an n value from 1 to 6. This is known as the principal quantum number.
• The second, ℓ, describes the subshell (0 = s orbital, 1 = p orbital, 2 = d orbital, 3 = f orbital, etc.).
  • The value of ℓ ranges from 0 to n − 1. This is because the first p orbital (ℓ = 1) appears in the second electron shell (n = 2), the first d orbital (ℓ = 2) appears in the third shell (n = 3), and so on. A quantum number beginning in 3, 0, … describes an electron in the s orbital of the third electron shell of an atom.
• The third, m_ℓ, describes the specific orbital (or "cloud") within that subshell.*
  • The values of m_ℓ range from −ℓ to ℓ. The s subshell (ℓ = 0) contains only one orbital, and therefore the m_ℓ of an electron in an s subshell will always be 0. The p subshell (ℓ = 1) contains three orbitals (in some systems, depicted as three "dumbbell-shaped" clouds), so the m_ℓ of an electron in a p subshell will be −1, 0, or 1. The d subshell (ℓ = 2) contains five orbitals, with m_ℓ values of −2, −1, 0, 1, and 2.
• The fourth, m_s, describes the spin of the electron within that orbital.*
  • An electron can have a spin of ±½, m_s will be either, corresponding with "spin" and "opposite spin." Each electron in any individual orbital must have different spins, therefore, an orbital never contains more than two electrons.

* Note that, since atoms and electrons are in a state of constant motion, there is no universal fixed value for m_ℓ and m_s values. Therefore, the m_ℓ and m_s values are defined somewhat arbitrarily. The only requirement is that the naming schematic used within a particular set of calculations or descriptions must be consistent (e.g. the orbital occupied by the first electron in a p subshell could be described as m_ℓ= −1 or m_ℓ = 0, or m_ℓ = 1, but the m_ℓ value of the other electron in that orbital must be the same, and the m_ℓ assigned to electrons in other orbitals must be different).

Bond Strength/Bond Length/Bond Order

Bond	# of electrons	Bond Order	Bond Strength	Bond Length
Single	2	1	Weakest	Longest
Double	4	2
Triple	6	3	Strongest	Shortest

Important points to remember about bond enthalpies:

• Bond enthalpy is the energy required to break a bond
• The stronger the bond, the higher the bond enthalpy
• Bond enthalpy is always positive (endothermic)
• Bond formation, EXOthermic, energy out
• Bond breaking, ENDOthermic, energy in

Trends that Affect Boiling Point (ORGANIC)

http://masterorganicchemistry.com/2010/10/25/3-trends-that-affect-boiling-points/

Molecular Forces of Attraction:

http://library.thinkquest.org/C006669/data/Chem/bonding/inter.html

Buffer Solutions

A buffer solution is an aqueous solution consisting of a mixture of a weak acid and its conjugate base or a weak base and its conjugate acid. It has the property that the pH of the solution changes very little when a small amount of strong acid or base is added to it. Buffer solutions are used as a means of keeping pH at a nearly constant value in a wide variety of chemical applications. Many life forms thrive only in a relatively small pH range; an example of a buffer solution is blood.

Obviously......***POINT: Be able to RECOGNIZE particular ions together as composing a buffer system, know that addition of STRONG/WEAK base (6 items on previous table) will only inc. or dec. the pH SLIGHTLY.

Phase Diagram, Vapor-Liquid Equilibrium

Vapor-Liquid Equilibrium

- bottom curve LIQUID, top curve VAPOR!!!!!!!!

- temperature vs. mole fraction (will usually have constituents A & B, b/w 0-1 like Raoult's Law Diagram)

Kaplan Pains In My Ass

azeotrope: a mixture of two or more liquids in such a ratio that its composition cannot be changed by simple distillation. This occurs because, when an azeotrope is boiled, the resulting vapor has the same ratio of constituents as the original mixture.

Positive and negative azeotropes

Each azeotrope has a characteristic boiling point. The boiling point temperature of an azeotrope is either less than the boiling point temperatures of any of its constituents (a positive azeotrope), or greater than the boiling point temperatures of any of its constituents (a negative azeotrope).

A well known example of a positive azeotrope is 95.63% ethanol and 4.37% water (by weight).^[3] Ethanol boils at 78.4°C, water boils at 100°C, but the azeotrope boils at 78.2°C, which is lower than either of its constituents.^[4] Indeed 78.2°C is the minimum temperature at which any ethanol/water solution can boil at atmospheric pressure. In general, a positive azeotrope boils at a lower temperature than any other ratio of its constituents. Positive azeotropes are also called minimum boiling mixtures or pressure maximum azeotropes.

Point: MINIMUM BOILING AZEOTROPE: Constituents NOT strongly attracted to each other.

An example of a negative azeotrope is hydrochloric acid at a concentration of 20.2% and 79.8% water (by weight). Hydrogen chloride boils at −84°C and water at 100°C, but the azeotrope boils at 110°C, which is higher than either of its constituents. The maximum temperature at which any hydrochloric acid solution can boil is 110°C. In general, a negative azeotrope boils at a higher temperature than any other ratio of its constituents. Negative azeotropes are also called maximum boiling mixtures or pressure minimum azeotropes.

Colligative Properties (Quantity, not identity, matters)

Since Colligative Strength depends on the # of particles in solution, it can often be determined from its van't Hoff/ionization factor (i)!

Unlike molarity, MOLALITY is independent of temperature and pressure! (Only one purpose: to have units of moles per kg)

MOLALITY = MOLES solute / KG solvent!!! Do not screw up!

Molarity always SLIGHTLY LOWER than Molality (because denominator contains BOTH the solute & the solvent)

VAPOR PRESSURE

- As temperature increases, vapor pressure increases

- The weaker a substance's intermolecular force (IMF), less energy need to leave the liquid, and thus HIGHER the vapor pressure/more easily it evaporates (ex: diethyl ether vs. H2O: see below)

- thus, HIGHER the Vapor Pressure, LOWER the Boiling Point! (also see below)

http://www2.bakersfieldcollege.edu/mdaniel/ch2a/ppt/VPressure.htm

1) VAPOR PRESSURE DEPRESSION

http://www.youtube.com/watch?v=0ZwknpcwTyQ

Adding more solute to a solution will DECREASE its Vapor Pressure

WHAT you put in solution and HOW MUCH you put into solution will affect changes to Vapor Pressure (count "molal", ex: C6H12O6, NaCl, CaCl2)

ex: Adding salt to boiling water:
- actually going to take a LONGER time to boil (since the vapor pressure has been depressed, takes for heat and time to reach the solution's boiling point)
- BUT, more HOT water molecules, bound to the solute particles, will STAY in the liquid phase INSTEAD of jumping to the gas/vapor phase, so the "pasta" will COOK FASTER!

- High vapor pressure out by beach (humid atmosphere), Low vapor pressure where dry at high altitudes (Not humid atmosphere)

2) BOILING POINT ELEVATION

Boiling point when Vapor Pressure = Atmospheric Pressure

Boiling Point DECREASES with altitude (ex: 100°C in New York, 69°C on Mt. Everest)

- boils faster, but takes longer to cook because not hot enough!

For every mole solute in kg solvent, the BP is raised by a certain amount ---> BP is proportional to the MOLALITY of a solution

***but remember that molality (m) is independent of temp. and pressure...

...

RAOULT'S LAW

Sweet chem dude again :) http://www.youtube.com/watch?v=PKgpumIUfyk

"Raoult's Law Graphs: LINEAR addition of partial pressures (concentration of gases) dependent on changing mole fractions. (No bendy lines)"

Effect of pH on Solubility

ex: CaCO3 in Oyster shells dissolves more strongly/easily in ACID...

http://www.youtube.com/watch?v=Lb8888u6chI

"But don't eat laxatives just to get calcium" hahaha

pH also affects its solubility – in an acidic solution, the equilibrium of the dissociation reaction of calcium fluoride is shifted more to the right as negative fluoride ions are removed, thus forcing the reaction in the direction of calcium fluoride dissolution. Note that pH does not affect the solubility of all salts. Typically, only weakly-soluble salts have pH-dependent solubilities. Examples include many hydroxides and carbonates.

http://www.mcatquestion.com/findquestion.php?arg1=1042

*Really interesting "Effects of pH on Solubility" BACTERIA/TEETH/CAVITIES/FLOURIDE example in Ebbing-Gammon (746)!!!

Ksp - Solubility equilibrium

Passage: The solubility of a solid compound such as a salt refers to the quantity of it that must be added to a particular volume of solvent to form a saturated solution. A solubility equilibrium results when a solid or gaseous compound is in chemical equilibrium with a solution of that compound. At equilibrium, the solution is saturated. The concept of solubility equilibrium is based on the assumption that when a solid dissolves in water or another solvent, it dissociates into the smaller, constituent units from which it was formed. Consider the salt calcium fluoride. When it dissociates, it produces three constituent atoms: one calcium atom (molar mass 40 grams/mol), and two fluorine atoms (each of molar mass 19 grams/mol).

Molar solubility is a term that refers to the maximum number of moles of solute that will dissolve in a liter of a solution before it becomes saturated. The molar solubility of calcium fluoride (CaF₂), for example, is 2.0 x 10^-4 moles per liter.

The solubility product constant (K_sp) is an important constant used to calculate molar solubility, and this constant refers to the product of the concentrations of ions in the equilibrium, each raised to the power of its coefficient in the equation.

Question 1: Calculate the K_sp of calcium fluoride.

(a) 1.6 x 10^-11
(b) 3.2 x 10^-11
(c) 4.8 x 10^-11
(d) 6.4 x 10^-11

Explanation: As stated in the text, the molar solubility of calcium fluoride is 2.0 x 10^-4moles per liter.

CaF₂ dissolves and dissociates as follows:

CaF₂ (s) ⇔ Ca²⁺ (aq) + 2 F^- (aq)
K_sp = [Ca²⁺] [F^-]²

The ratio between CaF₂ and Ca²⁺ is 1:1, but that between CaF₂ and F^- is 1:2. Consequently, dissolution of 2.0 x 10^-4 moles per liter of CaF₂ leads to production of 2.0 x 10^-4 moles per liter of Ca²⁺, but 4.0 x 10^-4 moles per liter of F^- in solution.

Insert the appropriate values into the K_sp equation:

K_sp = [Ca²⁺] [F^-]²
= (2.0 x 10^-4) (4.0 x 10^-4)²
= 3.2 x 10^-11

Oxidation Numbers, Oxidation-Reduction (Redox)

Determining Oxidation Numbers: http://www.youtube.com/watch?v=1ojEvef9oOw

Balancing Redox Reactions (ugggggh): http://chemistry.about.com/od/generalchemistry/ss/redoxbal_5.htm

Chem dude marry meeeeeeee:

1) http://www.youtube.com/watch?v=zcVLtoAdyd0&feature=related

2) http://www.youtube.com/watch?v=1ykHB_oGqw0

3) http://www.youtube.com/watch?v=STFiBTkj9RU&feature=related

WikiPremed: http://www.wikipremed.com/mcat_course.php?code=0214000200000000

***H2O is a reducing AND oxidizing agent!

Internal Energy (1st Law of Thermodynamics) & Sign Rules

http://www.wikipremed.com/01physicscards.php?card=565

q (+) = heat absorbed (energy is added to the system)

q (—) = heat evolved (energy is subtracted from the system)

W (+) = work done on the system (energy is added to the system)

W (—) = work done by the system (energy is subtracted from the system)

liter atmosphere (L·atm)

a unit of work or energy used in the study of confined gases. The behavior of gases is described, to a first approximation, by the ideal gas law PV = nRT. The ideal gas law is really an energy equation in which the left hand side, pressure P (in atmospheres) times volume V (in liters), measures the potential energy in the confined gas. 1 liter atmosphere is equal to approx. 100 joules...

******uggggghhhh case: W = P x dV = P (atm) x V (L) x (100J/l*atm)

Hemoglobin and the Oxygen-Dissociation Curve (IB)

- "Partial Pressures" of O2 and CO2 are measurements of their concentrations

- As O2 binds, conformational change makes it easier for other O2's to join (4 in total, 4 heme groups per hemoglobin)

- As O2 leaves, makes it easier for other O2's to leave

- When CO2 is produced it diffuses into RBC, where it reacts with H2O and is converted into Carbonic Acid via carbonic anhydrase enzyme, ****the acid then dissociates into H+ and HCO3-

- The H+ ions made the blood more acidic which causes oxyhemoglobin to dissociate and release O2

- The HCO3- ions are pumped through the membrane of the RBC and into the plasma where they combine with Na+ to form NaHCO3

- To ensure that the RBCs remain uncharged, Cl- ions pass into them. This is known as the chloride shift!

- When the RBCs reach the lungs, the NaHCO3 combines with H+ to form H2O, CO2, and Na+

- The CO2 is then released from the body during exhalation

Partial Pressure of CO2

- As cells respire, the pO2 decreases, and the pCO2 increases

- An increase in the pCO2 causes Oxyhemoglobin to give up its O2 more readily

- This is because when the CO2 is converted to acid it produces H+ ions which lowers the pH of the blood

- The Oxyhemoglobin then dissociates, giving up its O2 so that the Hb can bind to the H+ ions to prevent a change in pH

- Therefore Hb acts as a buffer by taking up the H+ ions and forming "Hemoglobinic Acid"

BOHR EFFECT (shift in affinity graph)

- more oxygen released with increase in CO2 and lowering of pH levels

- as pCO2 increases, the dissociation curve shifts to the right & down

So Overall:

- When O2 diffuses into the lungs there is a high PP of O2, so it will load onto Hb forming Oxyhemoglobin

- The O2 is then carried in the blood to respiring cells that have a low pO2 and a high pCO2

- So the Oxyhemoglobin releases the O2 because of the low pO2 and ALSO because of the high pCO2 which causes a DROP in pH

- The O2 is used by cells for respiration and the Hb binds to the H+ ions to prevent changes in pH

The composition and O2 carrying capacity differs among organisms...

Leslie: http://www.interactive-biology.com/2643/061-the-bohr-effect/

Transport of Respiratory Gases: http://www.youtube.com/watch?v=Qrvrs6RXxwY

Biochem dude: http://www.youtube.com/watch?v=DgelvyH7iB8&feature=related

VSEPR (Molecular Geometry)

Examples on Wiki page (Pink & White table)

http://en.wikipedia.org/wiki/VSEPR_theory

Other VSEPR Chart:

http://www.sfponline.org/Uploads/15/vsepr.gif

http://misterguch.brinkster.net/VSEPR.html

VSPR FLASHCARDS (quizlet)

http://quizlet.com/4958820/vsepr-example-models-flash-cards/

D-hybridization

http://forums.studentdoctor.net/showthread.php?t=594974

Sweet chem dude:

http://www.youtube.com/watch?v=o2MWDqs0wXA

http://www.youtube.com/watch?v=bZT_Xck8IDQ&feature=relmfu

Ionization

- The loss of an electron to FORM A +++CATION+++!!!

- Always ENDOthermic, must always supply energy!

Chemistry Randos

HIGHER THE BOND ENERGY, SHORTER THE BOND (inverse)

Bond length is also inversely related to bond strength and the bond dissociation energy, as a stronger bond is also a shorter bond, however, there are also few exceptions (Ex, H-H and H-O, the latter one has longer and stronger bond).

SPECIFIC HEAT (Heat Capacity, C)

***"the amount of energy required to raise 1g of that substance by 1 degree Celsius"

- larger the value, harder it is to raise the temp (ex: wood's 2.1 > mercury's 0.1)

Redox Counterintuition

	Oxidizing Agent	GAINS e-s in rxn
	Reducing Agent	LOOSES e-s in rxn

Lowest Freezing Point (makes no sense but remember)

The solution with the HIGHEST concentration of particles (CaCl₂, NOT NaCl) will have the LOWEST freezing point.

Higher K_sp means MORE soluble…

Spectrum

Electron Configuration & Decay

isoelectronic: same electron config (ex: F- & Ne)

Config for anions (move to RIGHT x spaces), cations (move to LEFT x spaces)

*****Transition Metals will lose its valence S electrons before losing and d electrons, so GET RID OF LAST "4S e's" AND PUT THEM IN THE LAST D ORBITAL!!!!!!!!!! (Even though 4s should be lower energy than 3d...TM's more stable with unfilled 4s and quasi-filled 3d orbital, rather than fillied 4s orbital...)

"I dont think there is a hard rule for transition metals which makes it a lot trickier. Some of them have d orbitals that are degenerate with the 4s orbital (same energy level). In some cases, it is better to have all half filled orbitals like 3d5 via Hund's rule. Supposedly this makes it more stable than say 4s2 3d3 and this explains why some orbitals can lose 4s electons before 3d ones even though 4s is lower in energy. Others can be different where the 3d orbital is at a higher energy level than the 4s orbitals."

diamagnetic: all of its e's (even # or all e-'s PAIRED) spin-paired, NO net magnetic field, REPELLED by a magnetic field

paramagnetic: all of its e's (odd-numbered or some e-'s UNPAIRED) are NOT spin-paired, ATTRACTED to a magnetic field

atomic emission spectrum: light emitted when when an atom's electrons FALL to their ground states

atomic absorption spectrum: light absorbed when an atom's electrons are EXCITED to higher energy levels

"Bohr atom" has only 1 electron...so count scenarios properly (Model for the Hydrogen atom)

In balancing ADDITION of alpha particle, balance out equation of mass and atomic numbers with this:

Alpha decay: Reduces the parent’s atomic number by 2 and mass number by 4 (releases an alpha particle = HELIUM atom: 2 protons and 2 neutrons). Any element with atomic number greater than 83 will automatically undergo alpha decay and start releasing protons/neutrons in the form of alpha particles.

http://www.youtube.com/watch?v=TEPVL-3DEtg

- Decreases the number of neutrons AND protons in large nucleus

Beta decay: Neutron decomposes into a Proton (and Electron), or vice versa via weak nuclear force

http://www.youtube.com/watch?v=1j-eDPLSBm0

*Mass number stays the same!!

- β^- à TOO MANY neutrons

o Increases the number of protons

- ex: Carbon 12 vs. Carbon 14... Carbon 14 gains a P+, releases an E-

- β⁺ à TOO FEW neutrons

o Decreases the number of protons

Electron Capture: Converts protons into neutrons

- nucleus draws in inner-shell electron, P and E react to form a Neutron

*Mass number stays the same, only Atomic number changes!! (ex: Rb to Kr)

http://www.youtube.com/watch?v=mhhAXQ5euYw

- Decreases number of protons, porque hay demasiado!

Gamma decay: Simply the expulsion of energy. Does not change the identity of the nucleus. Gamma photons emitted so atom can relax to its ground state.

- Gamma rays are emitted by the nucleus! and are often used in medicine to KILL CELLS

http://www.mcatquestion.com/findquestion.php?arg1=1044

one of like a trillion HALF-LIFE EQUATIONS: