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26 Cards in this Set
- Front
- Back
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oxidation
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atoms that lose electrosn
OIL rig |
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reduction
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atoms that gain electrons
oil RIG |
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oxidation states
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-possible charge values that an atom may hold within a molecule
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Oxidation states
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Elements: 0
Flourine: -1 Hydrogen: +1 Hydrogen with metal" -1 Oxygen: -2 (except with Hydrogen Peroxide) |
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Oxidizing agent
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what has been reduced
-can be compounds or atoms while what is being oxidized or reduced are only atoms |
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Reducing agent
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what has been oxidized
-can be compounds or atoms while what is being oxidized or reduced are only atoms |
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if a half reaction has a negative oxidation potential, is it a spontaneous reaction?
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NO, half reactions with positive oxidation potentials oxidize spontaneously.
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Au3+ (aq) + 3e- --> Au (s) 1.5 potential
What is the oxidizing potential? |
Since the equation shows electrons being gained, it is a reduction reaction. The oxidation would be -1.5.
-these are intensive properties and do not change with quantity...do not multiply by # moles |
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Balancing Redox Reactions
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1) divide into half reactions
2) Balance all elements besides H and O 3)add H20 to one side until O atoms are balanced 4) add H+ to other side until H are balanced Add e- to one side until charge is balanced -multiply by integers to equillibriate electrons on both sides |
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galvanic cell
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-converts chemical energy to electrical energy,
-oxidation occurs at the anode, anox -reduction occurs at the cathode -anode is negative -cathode is positive -two terminals of the galvanic cell must be the same material -electrons flow from anode to cathode creating a current that flows in the opposite direction -cell potential for a galvanic cell is always positive -EMF depends on half reactions, concentrations of reactions and products and temperature |
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Cell potential in a galvanic cell
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-aka electromotive force (emf)
-potential difference between terminals |
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Salt Bridge in a Galvanic Cell
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-liuqid junction that minimizes potential difference created by ions of two different solutions in a cell
-not necessary when electrodes are in contact with same solution |
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stabdard state of emf of galvanic cell
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-found by subtraction potential of reduction hal reaction at the anode from teh potential of the reduction half reaction on the right or cathode
Cathode on right anode on left |
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Free Energy and chemical energy
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Positive cell potential= spontaneous reactoin
ΔG= -nFEmax n= # moles electrons transferred F= Faradays constant: 96,486 C/mol E= voltage nF=total charge charge X voltage = work w=qv -non PV work -ΔG = work done by system |
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Free energy for non standard conditions
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ΔG = ΔGmax + RTln(Q)
Q= reaction quotient -if we have equillibrium ΔG =0 then plugging that in above ΔGmax= -RTln(K) if K=1 ΔG =0 if K >1 ΔG <0 if K <1 ΔG >0 this means if K>1 the reaction is spontaneous at standard state where starting concentrations are exactly 1M |
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Whe value of all of the following are reversed when a reaction is reversed EXCEPT
1) rate constant 2) enthalpy 3) gibbs energy 4) reaction potential |
-rate constant is rarely equal forward and backward..only at equillibrium
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Electrolytic cell
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-galvanic cells have a positive potential but electrolytic is the only one that can have a negative potential
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Concentration Cell
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-limited form of a galvanic cell with a reduction half potential taking place in one half while the exact reverse is taking place in other half of cell
-Emax=0 -current will flow from more to less concentrated side -use nernst equation to substitude equations |
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Electrolytic Cell
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- negative potential
-cathode is marked negative and anode is marked positive an-ox red cat still holds -hooked to power source |
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161: Which of the following statements is true concerning the galvanic cell at 25 C?
-Magnesium reduced at cathode -Concentrations of ions are 1M -reaction is spontaneous |
-reactions in galvanic cells are always spontaneous
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Electron flows to cathode or anode in galvanic cell
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-reduction takes place at cathode..electrons flow to cathode
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Nernst Equation and concentration cell
E= Enaught -.06/n(log(x/y)) If potential is .12 V and a concentration of .1 M Ag+ at anode what is concentration of Ag+ at cathode? |
Answer:
In a concentration cell Enaught = 0 bc the reduction half reaction is equal to reverse of oxidation reaction. E= -.06/n (logx/y) .1M at anode =X E=.12V n=1 bc 1 e- is transferred y must be smaller than x bc log of that number has to be negative and therefore that fraction must be less than one. that fraction needs to equal 10^-2 so y=10 |
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How do you find mass given current, i, time t, F faradays constant?
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i= C/s F=C/mole e- transferred
t- s i/F= moles/s it/F= moles then multiply moles by molecular weight |
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Locations of strongest oxidizing agent and strongest reducing agent
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-strongest oxidizing agent is on the upper left while strongest reducing agent is on the bottom right.
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Reactions at standard conditions
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ΔG =ΔG naught +RTln(Q)
Q=1m lnQ=0 ΔG =ΔG naught |
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What is the potential E at equillibrium?
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At equillibrium, no reaction is favored so there is no potential.
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