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Definitions |
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q(charge)E=
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-w
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reduction
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gaining electrons
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____ accelerates rusting
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Salt
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moles of electrons
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n
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emf=potential difference (V)=
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work (J)/charge (C)
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Half-reactions are always assigned standard ________ potentials.
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reduction
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Energies, enthalpies, and free energies are always defined relative to a __________ state.
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reference
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Reduction occurs at the ________.
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cathode
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left side
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Redox reduction electron placement
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Electrolysis
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Making a nonspontaneous reaction spontaneous by adding an external electrical charge
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Anode
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Electrode where oxidation (acquisition of electrons) occurs.
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In a concentration cell, E*=_______ because under standard conditions, the concentration would be the same on both sides
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0
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The relationship between cell potential and concentration can be used to determine ________ __________ for reactions that are not redox reactions.
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equilibrium constants
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Corrosion involves the __________ of metal.
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oxidation
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Oxidation involves a ________ of electrons.
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loss
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In a concentration cell, electrons flow towards the side with a __________ concentration of cations.
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greater
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oxidation
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The more negative the reduction potential, the larger the tendency the substance has to go through __________.
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0
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At eq. E cell = ?
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Most metals develop a thin _____ coating that protects their internal atoms against further corrosion.
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oxide
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__________ is the voltage required in excess of the expected value.
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overvoltage
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_________ is the returning of metals to their natural state (ores).
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corrosion
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w/wmax x 100% =
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efficiency of the cell
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All standard reduction potentials are taken at ____ degrees Celsius and are measured in ______.
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25; volts
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T/F: When the stoichiometry of a half-reduction is doubled, the cell potential also doubles.
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False
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1.1 V
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Standard reaction Voltage of Danielle Cell
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total charge = nF
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total charge = ?
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Electrochemistry
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The conversion of chemical energy into electrical energy (that involves the transfer of electrons).
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oxidant
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oxidizing agent in a redox reaction, this will be reduced
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reductant
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reducing agent in a redox reaction, this will be oxidized
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electromotive force
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(emf) aka cell potential, potential difference btw the terminals when they are not connected
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Electrodes that are sensitive to the concentration of a particular ion are called
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ion-selective electrodes
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The typical automobile uses a ____ storage battery of ______ cells connected in series.
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lead; six
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A _____________ is adjusted so that no current flows in the cell circuit.
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potentiometer
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The maximum potential must be found at _______ current.
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zero
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A platinum electrode is often used in a standard hydrogen electrode as a cathode because it is a chemical ________ conductor.
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inert
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T/F: The oxidation of most metals is spontaneous.
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true
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Pure water contains so few ____ that only a negligible current can flow.
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ions
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The reaction of methane with oxygen is exothermic/endothermic?
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exothermic
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When dealing with half reactions, first assign _________ __________ to all elements, then add H+ or OH- as needed, and then add ___ as needed.
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oxidation states, H2O
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Cathode
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In a danielle cell this metal's mass increases as well as its concentrations as it becomes more negatively charged than positively.
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Nernst eqn
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E = Eo - (RT/nF)ln(Q)
expresses the relationship btw chemical concentrations and potential difference
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galvanic cell
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aka voltaic cell, made of multiphase series of components w/ no component occurring in more than 1 phase but all conduct electricity but 1 is impermeable to electrons
*cell potential is always positive*
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____ is used to coat steel in a process called galvanizing and does not form an oxide coating but is dissolved in place of the iron.
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Zinc
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A cell will run in the direction that produces a ________ cell potential.
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positive
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A salt bridge filled with an ________ or a porous disk helps to maintain a net charge of ______ in each compartment.
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electrolyte; zero
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Diagonal Rule
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Pick one on the list for reduction potential, everything below it will create a sontaneous cell
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How does galvanizing work?
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Since metals exposed to environment oxidize over time (especially when exposed to salt water b/c conducts electricity well), galvanizing used to prevent this. It involves adding sacrificial metal (more reactive metal) to be preferentially oxidized over metal being preserved.
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electric potential, E
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a potential associated with any redox reaction, can be separated into the oxidation and reduction component
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positive cell potential indicates ___ free energy
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negative
meaning rxn is spontaneous
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1 volt=
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1 joule of work per coulomb of charge transferred
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A cell in which both compartments have the same components but at different concentrations is called
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a concentration cell
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Reduction Potential
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Value looked up on chart also known as E cell standard or emf. It cannot be measured w/out a zero point.
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What are some biological reducing agents and their specific purposes?
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NADH reduces carbonyls, FADH₂ reduces alkene double bonds
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galvanic cell symbolized -
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T-E-I-E'-T' where T are the terminals, E are the electrodes, and I is the ionic conductor (often salt bridge)
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standard state cell potential
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sum of the standard state potentials of the corresponding half reactions
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transition metal oxidation states
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change according to the atoms with which they are bonded
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T/F: Gold corrodes in air.
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False because gold has a standard reduction potential of 1.5 V, which is significantly larger than that for oxygen (1.23 V).
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The driving force on the electrons is called the ______ __________ or the __________ __________ (emf) of the cell.
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cell potential; electromotive force
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E cell = E cathode - E anode
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Ecell standard = ?
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How can you identify species that will breakdown easily?
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High oxidation/low reduction potentials are large - numbers in the table. Lowest ionization energy is highest oxidation potential. Some examples of this are Alkali and Alkaline earth metals like sodium, potassium, and magnesium.
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anode in a galvanic cell
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where the oxidation half rxn takes place
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cathode in a galvanic cell
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where the reduction half rxn takes place
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What is the net equation for the electrolysis of water?
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2H2O --> 2H2 + O2
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How do you calculate cell potential (voltage or emf associated with redox rxn pairs)?
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Add together the reduction potential and oxidation potential, but flip the sign if a half reaction is being reversed to look like the overall rxn.
*NOTE: The values are listed in terms of voltage, which is independent of number of electrons in the reaction, so do not multiply the emf by an integer, even if it is necessary to balance the atoms.
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free energy and cell potential eqn
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delta(G) = -n*F*Emax
n is the moles of e' transferred, F is Faraday's constant, E is the cell potential
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E cell = E cell standard - RTlnQ/nF
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E cell = ? (Nerst Equation)
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How do you calculate the free energy change (conversion from voltage to Energy)?
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*Unlike emf, energy associated with electrochemical cells (free energy) depends on # of e⁻'s (J/mol)
The equation above gives the energy per mole of e⁻'s in electrochemical cell. nFE(cell) is electric work done.
Favorable redox rxn= +emf, -ΔG
n=#e⁻'s per rxn, F=96500 Coulombs/mole
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atom with a -2 oxidation state
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oxygen (except when it is a peroxide like H2O2)
group 16 elements (oxygen family)
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Maximum work a cell can perform
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Maximum work = -1 * (moles of electrons) * F * (cell potential)
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What is the Nernst equation and what does it tell us?
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*Read log of oxidized (anode) over reduced (cathode) concentration
I tells us the effect of half-cell concentrations on voltage quantified by relationship between the anode and cathode.
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in what direction will current flow in the concentration cell?
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think about which will create the greatest entropy - the more concentrated side will try to become less concentrated and the e's will flow accordingly
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what would happen if a galvanic cell didn't have a salt bridge
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the solns of the galvanic cell would mix providing a low resistance path for e's to move from the anode to the cathode effectively short circuiting the cell and leaving it with a potential of zero
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