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42 Cards in this Set

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What is the Half Reaction Method for Balancing Equations in Acidic Solutions?
(1) assign oxidation numbers to each atom to know what is oxidized/reduced; (2) split the skeletal equation into two (reduction & reduction); (3) complete and balance each half reaction, balance O with H2O on the other side, balance H with H+ on the other side, balance charge with e- on the positive side; (4) combine the reactions, multiplying each half reaction by whatever factor cancels e-, and simplify by removing species that occur on both sides
What is the Half Reaction Method for Balancing Equations in Basic Solutions?
Follow steps 1-4 for acidic solutions; (5) note the number of H+ ions in the equation, and add that number of OH- to both sides; (6) remove any H2O's on either side of the equation
What is the difference between a Voltaic Cell; and an Electrolytic Cell
A voltaic cell uses a spontaneous reaction to generate an electric current. An electrolytic cell is one in which an electric current drives a nonspontaneous reaction.
Why is a salt bridge important?
It connects the two half cells in a voltaic cell, this allows the flow of ions and prevents direct reaction between the half cell reactants.
What is a Cathode?
The cathode is the half cell with the electrode where reduction occurs. The anode has a positive sign.
What is the Anode?
The anode is the half cell with the electrode where oxidation occurs. The anode has a negative sign.
Why is do electrons flow from the anode to the cathode in a Voltaic cell?
Because electrons are given up at the anode (oxidation) and are used at the cathode (reduction).
What is the form of notation for a voltaic cell?
Catalyst | Anode Terminal | Anode Electrolyte || Cathode Cathode Electrolyte | Cathode Terminal

Example:

Zn(s)|Zn2+(aq) || Cu2+(aq)|Cu(s)
How do you write the overall cell reaction from the cell notation?
Write out the half cell reactions, including the e-, then balance the reactions.
What is Potential Difference?
Electricity flows from high to low electric potential. The potential difference is the difference between these two points. It is measured as Volts (V).
What is Electrical Work, and how is it Calculated?
Electrical work is the work needed to move an electric charge through a conductor. Electrical work (J) = charge (c) x potential difference (v)
What is the Faraday Constant?
The magnitude of charge on one mole of electrons. The amount of work done by a voltaic cell in moving 1 faraday of charge from one electrode to another is calculated from the equation: w = -F x V. Work is negative because the cell loses E as it does work.
What is the Cell Potential (emf or Ecell) ?
The maximum potential difference between the electrodes of a voltaic cell. Because it takes energy to drive the current, the Ecell will equal its max value only when no current flows.
Calculate Wmax of a Voltaic Cell for a Molar amount of Reactant?
wMax = -nFEcell; also note that wMax = ΔG°
Why is the Cell Potential important?
It is a measure of the driving force of the cell reaction. It is the sum of the potentials for the reduction and oxidation half reactions.
Why is Electrode Potential independent of the amount of Species in a Reaction?
It is an intensive property.
What are Standard State Conditions for the Standard Cell/Electrode Potential?
Solute concentrations of 1M each, gas pressures of 1atm, and temperature of 25C
What are the Strongest Oxidizing Agents, and the Strongest Reducing Agents on the Table?
The strongest oxidizing agents are along the bottom left (F2(g) + 2e-) and the strongest reducer is the top right (Li(s))
What are two ways to calculate Cell Potential from Standard Potential values?
(1) Add the half reactions and standard potentials (2) Ecell = Ecathode - Eanode where E = standard state
How do you calculate the Equilibrium Constant from the Cell Potential?
ΔG° = nFE°cell or;
E°cell = (0.0592/n) log K
What two factors determine the Cell Potential?
Concentrations of ions and gas pressures.
What formula relates E°cell to Ecell at other ion concentrations and pressures?
The Nernst equation:

Ecell = E°cell = (0.0592/n) log Q
How do you set up a Voltaic Cell to determine the pH of a substance?
Use the test solution as an electrolyte for a hydrogen electode, then bubble in gas at 1 atm. Connect the Hydrogen electrode to a zinc electrode.

Zn|Zn2+(1 mol) || H+(test solution) | H2 (1 atm) | Pt
What form of the Nernst Equation solves for pH?
pH = (E°cell - Ecell)/0.0592; where E°cell refers to standard cell potential, Ecell refers to actual cell potential, and 0.0592 is equal to the expression RT/F (all constant at constant T) merged with the conversion from ln to log
What is the setup for a Hydrogen Electrode?
A platinum catalyst plate is attached to an electrode and submerged in water. Then Hydrogen is bubbled over the plate, releasing h+ ions or forming H2(g) depending on which half reaction is taking place in the cell. The cathode notation would be: H+(aq)|H2(g)|Pt; the anode reaction would be: Pt|H2(g)|H+(aq)
What is Electrolysis?
The process of producing a chemical change in an electrolytic cell.
Describe the Process of Electrolysis of Molten Sodium Chloride.
An anode and cathode are placed in molten NaCl (801°C). At the anode Cl- is oxidized to Cl2. In this way Sodium metal is extracted from Chlorine gas.
How does electrolysis of aqueous solution differ from electrolysis in a molten salt?
In molten salt you need only consider the ions from the salt, but in aqueous solution you need to consider that water is involved at one or both electrodes.
In the electrolysis of an aqueous solution, what species derived from water involve a change in change in oxidation state?
Water can be reduced to H2(g) and can be oxidized to O2(g). You can balance such half reactions by adding H+ to one side or another.
What species in a solution of Sulfuric Acid should you consider would involve a change in oxidation state?
Sulfuric Acid (H2SO4) ionizes into H+ and HSO4-, which further ionizes into H+ and SO42- Therefore the species you should consider are H+, SO42-, and H2O
What is Overvoltage?
In electrolysis half reactions occur far from equilibrium, so a larger voltage than predicted from the electrode potentials must be supplied. This occurs when the electrode potentials are close (within several tenths).
What are the possible species involved in half reactions of Sodium Chloride solution?
Na+, Cl-, and H2O
How are the amounts of substances released at the electrodes related to the total charge that has flowed in the circuit?
This relationship is stoichiometric, and includes a stoichiometric relationship between the number of electrons to the number of moles of product. Because you cannot directly measure electrons, the Faraday constant measures 1 mole of electrons via the charge that passed through the circuit.
What is the formula relating electric charge to current and time?
Electric charge (Coulombs) = electric current (amperes) x time (seconds).
What is important to remember about electrolysis of aqueous solutions?
They will involve species derived from water (H2, O2).
What species should you look at for the Electrolysis of Sulfuric Acid?
H+, SO42-, H2O
If given two oxidation potentials, how do you choose the anode and cathode?
The larger (less negative) oxidation potential is more easily oxidized, therefore it is the Anode.
What species should you look at for the Electroylsis of Sodium Chloride solution?
Na+, Cl-, H2O
In Aqueous Electrolysis, which half reaction should receive the H2O species?
Both
In Aqueous Electrolysis, where water and ion species are involved, how do you choose which possible cathode or anode half reaction is the true anode or cathode?
You need to look at the electrode potentials. For the Cathode, choose the larger (less negative) oxidation potential of thw two for the anode. For the Anode, choose the smaller (more negative) of the two.
How do you know if you are involved in the electrolysis of a molten salt?
The form of the salt will be (l), instead of aqueous.
What are the half reactions for H2O species?
The Oxidation reaction is H2O to O2:
2H2O -> O2 +4H+ +4E
The Reduction reaction is H2O to H2:
2H2O + 2e- -> H2 +2OH-