CHEM 0120 Lecture Notes - Lecture 1: Transition State Theory, Endothermic Process, Equilibrium Constant

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6 Feb 2017

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Key Points of Chemistry II
Chapter 12
Phase Changes
-Eah phase hage is aopaies  a stadad ethalp hage ΔH
-Dynamic equilibrium: molecules are entering and leaving a phase at equal rates
-To find heat of vaporization use the Clasius-Clapeo elates tep ad VP ΔH i Joules
-Boiling point is directly proportional to applied pressure
-Temperature does not change during a phase change
-Larger molecular weight = more IMF = higher boiling point = higher pressure
-Heat for phase hages: ΔH   + s    Δt
-Phase diagrams give the conditions of temperature and pressure at which each phase is stable
-Viscosity: resistance of a fluid to flow (decreases with heating and smaller molecules)
Intermolecular Forces
-Van der waals: the attraction of IMF between molecules (exists in every molecule)
-Ion-dipole: an ion and polar molecule
-Dipole-dipole: attractive force between polar molecules
-Hydrogen: a dipole-dipole force that occurs when an H atom is bonded to N, O, or F
-Ion-induced dipole: NP and ion; Dipole-induced dipole: NP and polar
-London-dispersion: only force that exists between non-polar molecules
-Polarizability: how easily the electron cloud of an atom can be distorted (small particles = low P because
they hold their electrons close)
Intramolecular Forces
-Ionic: cation-anion
-Covalent: nuclei-shared e pair (H-H)
Solid State
-Crystalline: well-defined shapes that occur in an orderly arrangement
-Coordination number: number of the nearest neighbors of a particles (SB: 6, BCC: 6, FCC: 12)
-There is a specific relationship between the length of a side and the radius:
-SB: R=L/2, BCC: R=(3)1/2/4 * L; FCC: (2)1/2/4 * L
-If given the density, use the mass to find the volume or L3
-To calculate mass of the cell: (# of atoms)(molecular weight)/(6.022x1023)
Chapter 13
-The solubility of a solute is the maximum amount that dissolved in a fixed quantity of a given solvent
-Substances with similar types of IMF dissolve in each other
-Two substance will dissolve if: the forces between molecules are the same or stronger than between
the individual molecule
-Solubility in water is high for smaller alcohols
-Solvation in water is called hydration and it is always exothermic
-Lattice energy is the energy needed to separate an ionic solution, larger molecules are more soluble
-When a solution forms, systems change toward a state of lower enthalpy and higher entropy
-All soluilities ae tepeatue depedet solids soluilit ieases ith tep, hile gases do’t
-Pressure has very little effect on the solubility of liquids and solids
-He’s La: epesses the uatitatie elatiosip etee P ad S Sgas= KH x Pgas) (S2 = S1 (P2/P1)
-Strong electrolytes (soluble salts, strong acids, and strong bases) conduct current because their solutes
separate into ions
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Non-volatile Solution
-These solutions contains solutes that are not ionic and do not dissociate
-Raoults Law: states that the VP of solvent above a solution equals the MF of solvent times the VP of the
pure solvent (Psolvent = Xsolvent*Posolvent o ΔP = Xsolute*Po)
Volatile Substances
-Whe a olatile sustae ehaes ideall, the follo Raoult’s La PT = XaPoa + XbPob)
-The presence of each volatile component lowers the VP of the other
-Moles fractions can also be used to find partial pressures: Xa = Pa/Pa+Pb
-The passage of solvent through a membrane from the less concentrated side to the more concentrated
-Osmotic pressure is the amount of pressure necessary to stop osmosis (OP = MRT)
-This is a colligative property because it depends upon the total concentration of particles
Chapter 16
Reaction Rate
-This is the change in concentrations of reactants or products as a function of time
-Larger concentration = faster reaction (more molecules colliding)
-Finely-divided reactant (more soluble) = faster reaction
-Higher temperature = faster reaction = more energy
Rate Law/Order
-Rate of reaction depends on the concentration of reactants (rate = k[A][B])
-The reaction order is the exponent to which the concentration of that species is raised, and it indicates
to what extent the concentration of a species affects the rate of a reaction, as well as which species has
the greatest effect
-A reaction has an individual order in each reactant (RA = k[A]x)
-First order (x=1): the rate doubles when [A] doubles
-Second order (x=2): the rate quadruples when [A] doubles
-Zero order (x=0): the rate does not change when [A] doubles
-To find the order: determine the average rate (R1/R2) and then rate = ([A]/[B])X
-The time it takes for the reactant concentration to reach half its initial value
-First order: t1/2 = ln2/k (independent of concentration)
-Second order: t1/2 = 1/k[Ao]
-Zero order: t1/2 = [Ao]/2k
Reaction Mechanism
-Reaction intermediate: a substance that is produced and consumed in a reaction so none is detected
when the reaction is finished
-The rate law of the rate-determining step (slow) is the rate law of the whole reaction
Collision Theory
-Particles must collide to react can only occur if the collision have the right orientation and energy
-Rate increases exponentially with temperature
-Steric factor correct orientation (p)
-The more complex the structure, the smaller the p-value
-Arrhenius equation k=Ae-Ea/RT
Transition State Theory
-Explains the reaction resulting from collision of molecules to form an activated complex
-Activation energy (Ea) an energy threshold colliding molecules must exceed to react
-With a larger Ea the rate of reaction decreases (need more energy)
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