Chem exam 2- electro/thermo chem

Ksp

solubility constant, determined through experiment, the dissolution of a compound or precipitation from solution (**rxn has two way arrow, stuff keeps dissolving/precipitating out, but at equilibrium it does so at same rate

Ksp equation

=[IonA]^a * [IonB]^b (NO solids included)

Morphine

comes from opium poppy sap, easily passes blood/brain barrier, is an alkaloid molecule, opium lead to war between britain/china, can easily be made into the less potent codeine or more potent heroin

Caffeine

has N-C bonds so it can cross blood-brain barrier, binds to adenosine transmitters, part of society’s shift from downers(opioids) to uppers for the industrial revolution and increased productivity

Ksp and solubility comparison

the salt with a smaller Ksp (*pay attention to exponent on # x 10^#) can dissolve less and will precipitate out before a salt with a larger Ksp

Solubility with a common ion

use ICE table and Xs, and use concentration of shared ion as the “initial” value (the X added to the initial usually cancels out)

Enthalpy

ΔH, heat of reaction, a state function, the heat change at a constant pressure, only thing that can tell if a rxn is endo/exothermic

ΔHf

heat of formation, Units: kJ/mol ; has a numerical value for all substances, is 0 for all elements in their standard states [O2(g), W(s), Hg(l), C(s), Br2(l), S8(s)]

ΔH calculation

ΔHproducts–ΔHreactants (for each part, the ΔH’s can be multiplied by stoichiometric factors & summed)

State function

Function whose value only depends on the present state and not path taken

Law of conservation of energy(1st law of thermo)

energy cannot be created or destroyed; consider reactions as isolated from the world=the system; the total energy of a system is constant [also, free energy (G) can do work or dissipate as heat]

(Little) q

represents transferred heat, + if system gains heat, – if system loses heat

Determining if endothermic

positive ΔH value

Determining if exothermic

negative ΔH value

ΔHsolvation

ΔHhydration – ΔHlattice (*the lattice in salts requires energy to break)

ΔHbond

ΔHrxn/(# of bonds)

Standard temp

298K (or 25 C)

Entropy

ΔS molecular randomness, units: J/mol*K, a quality (all physical processes involve order/disorder), a state function, also =Sfinal – Sinitial

ΔS at constant temp

=qrev(the heat constant of system)/T , the addition of q to system causes larger increase in ΔS at low temps (and smaller ΔS increases at high temps)

Estimating ΔS

-state (s<l<<g) -complexity & rigidity (rigid<flexible) -number of moles (especially for gas, more moles is more +)

Bismuth

Super heavy big Atomic mass, last element on periodic table that is not radioactive, Bi-213 used in targeted Alpha therapy for cancer, Pepto-Bismol made of bismuth subsalicylate ligand does hydrolysis in stomach and splits into salicylic acid (sort of in aspirin) and bismuth metal, taken for anti-inflammatory effects and coats stomach, bismuth sulfide forms in feces and appears black

Entropy of phase changes

ΔH/T (since phase changes are at equilibrium, ΔH=qrev), ΔSvaporization>>ΔSfusion, review graph (pg 17)

Second law of Thermodynamics

in any process the total entropy of the system always increases since universe is constantly expanding, all reactions proceed spontaneously in the direction that increases the entropy of the system(ΔH/T) and surroundings(-ΔH/T), AND all real processes further disorder the universe, AND movment from high to low pressure/concentration

Nitro compounds

addition of nitro group to organic molecule adds oxygen into molecule itself so it can burn without air, rapid energy release with stable final products like N2, the chinese made black gunpowder(saltpepper+charcoal+sulfur) but used it mainly for fireworks, Alfred Nobel became famous/rich from nitroglycerin(dynamite/TNT) that was used to clear land/mountains for transportation and impacted civil engineering, shifted warfare(artillery replaced hand to hand combat) **more info in notes but unstarred

Gibbs free energy

reaction is spontaneous if –, reverse spontaneous if +, and at equilibrium if 0 (*0 for all elements in standard state at 298K)

Standard conditions pressure

1atm

Standard conditions concentration

1.0M

Silicon (Si)

semiconductor, can be in photovoltaic solar cells (more info in notes pg18)

ΔG and Keq relationship

products favored ΔG

Meaning if Q=K

reaction is at equilibrium

Meaning if Q>K

reaction goes to the left (more reactants being made)

Meaning if Q<K

reaction goes to the right (more products being made)

Manganese (Mn)

super abundant, tiny cube controls photosystem II (giant protein for photosynthesis) and oxidizes H2O–>O2

Cathode

site of reduction (gain of e-)

Anode

site of oxidation (loss of e-)

4 types of rxns (gibbs-wise)

always spontaneous –H +S –G, reverse spontaneous +H –S +G, entropy driven & spontaneous at high temps +H +S ?G, enthalpy driven & spontaneous at low temps –H –S ?G

Hess’s law w/ gibbs

review

Voltaic cell basics

spontaneous, produces energy, uses materials, *for batteries

Electrolytic cell basics

reverse spontaneous, produces materials, uses energy, *for synthesis, (e- pumped in by adding voltage to make rxn proceed; G SHOULD be +)

E and G relationship

Eo = –G (means favorable when E is +)

Electromotive force

generation of force using e- (EMF)

Eocell equation

=Ecathode–Eanode

Voltaic cell diagram key features

e- flow on wire from anode (getting skinny) to cathode (getting thick). Include salt bridge w/ions on correct sides if needed, 2 containers, 2 electrodes connected by wire

Ruthenium (Ru)

used for solar energy (dye-sensitized solar cells, dyes the white TiO2 so that it can absorb light in the visible spectrum) [*sensitization=binding to semiconductor]

Disproportionation

self oxidation/reduction (several species are thermodynamically unstable with respect to redox, ex: hydrogen peroxide, copper), can be solved with kinetic stabilization

Kinetic stabilization

stopping disproportionation by adding a salt (with low solubility) to make the problematic ion precipitate out [ex: adding CuX to make Cu+ precip out]

Path function

does depend on path taken

Work

movement of charge through a potential difference , equal to delta G

Charge

measured in moles (avogadros x #e-)

Faradays constant

capital “F”, given, charge on a mole of e-

“n”

number of moles of e- (the e- that cancel out when combining half reactions)

Joule conversion

= coulombs x volts = C x V

Written cell

Reactantanode|Panode || Rcathode|Pcathode

When to use nernst

for nonstandard conditions for full and/or half reactions (ALL products & reactants not at 1atm, 1.0M), *special form of eqn for temp at 25 Celcius

Concentration cells

voltaic cell where both compartments have same components but at different concentrations (bc cell potentials depend on concentration), calculate to find spontaneous direction (*standard delta G and E cancels out bc equation is same on both sides)

Nobel prize winners and info

henri kagan & kenso soal, enantiomers (chiral pairs), discovered chirality and created enantiomer specific production process (product acts as chiral catalyst to make chiral copies so only one handedness produced)

chlorocarbons

refrigerants & thinning eggshells

biology example: nitrogenase enzyme redox cell components

Fe anode, stored carbs→H₂O+CO₂

Mo-Fe cathode, N₂+6H⁺→2NH₃ (used in amino acid synthesis)

disulfide bonds as ‘wire’

electrolytic fluid as ‘salt bridge’

electrolytic cells

need e- pumped in via voltage added to force rxn since G>0

cyclic voltametry

looks at redox potentials experimentally, vary potential and look for current change

has 3 electrodes: working(rxn of interest), auxilary(other half rxn), reference (its own mini rxn)

duck shaped graph, current increase until peak (peak is reduction), current decrease until valley (valley underneath is oxidation)

2 triangle graph

honda fujishima cell

BE ABLE TO DRAW

generates fuel, drawback is needs UV light

graetzel cell

BE ABLE TO DRAW

dye sensitized solar cell