Chapter 19 Electrochemistry Flashcards
Define Oxidation Reduction Reaction
Reactions in which electrons transfer from one reactant to the other
Define Oxidation
The loss of electrons
Define Reduction
The gain of electrons
The INCREASE in oxidation state of an atom is ____________
Oxidation
The DECREASE in oxidation state of an atom is ____________
Reduction
What is the oxidation state rule for a free element?
Oxidation state = 0
What is the oxidation state rule for a monoatomic ion?
Oxidation state = its own charge
What is the oxidation state rule for the same of oxidation states of neutral molecules and ions?
Neutral molecule oxidation state = adds up to 0
Ion oxidation state = adds up to its charge
What is the oxidation state rule for metals in compounds in group 1A and 2A
Metal group 1A oxidation state = +1
Metal group 2A oxidation state = +2
What is the oxidation state rule for nonmetals H and O?
H oxidation state = +1
O oxidation state = -2
Assign oxidation states to the following... I) Cl2 II) Na+ III) KF IV) CO2 V) FeSO4
I) 0 II) +1 III) 0 IV) 0 V) -2
Assign oxidation states to the following... I) Ag II) Fe3+ III) CH4 IV) Cr2O7 2- V) ClO4 - VI) CaH2
I) 0 II) +3 III) C: -4, H: +1 IV) Cr: +6, O: -2 V) Cl: +7, O: -2 VI) Ca: -2, H: +1
Define Half-Reaction Balancing Method
A form of balancing redox reactions where you separate the overall equation into 2 half reactions
Define Balancing Redox Reaction
When you balance both the mass and charge of the redox reactions
What are the 2 half reactions for Half-Reaction Balancing Method?
Half for oxidation and half for reduction
When balancing ACIDIC solutions, what do you add to balance O and H?
Add H2O to balance O and H+ to balance H
When balancing BASIC solutions what is the additional step you must take?
Neutralize H+ by adding enough OH- to each H+ and add the same number of OH- ions to both sides
Define Oxidizing Agent
A substance that causes the oxidation of another substance
Define Reducing Agent
A substance that causes the reduction of another substance
Oxidizing Agent is ____________, _______ electrons, and its oxidation state __________
Reduced; gains; decreases
Reducing Agent is ____________, _______ electrons, and its oxidation state __________
Oxidized; loses; increases
In the following reaction which element is the Reducing Agent and which is the Oxidizing Agent? 4 Na (s) + O2 (g) --> 2Na2O (s)
Na : Reducing Agent
O: Oxidizing Agent
Define Electric Currents
The flow of electric charge
What are the 2 ways electric currents are involved with chemical reactions?
I) Certain chemical reactions can product electricity
II) Electricity can make certain chemical reactions (nonspontaneous reactions) happen that would not happen otherwise
Define Current
The number of electrons that flow through the system per second
The unit for Current is…
Ampere (A)
What are the 2 types of Electrochemical Cell types?
I) Voltaic (Galvanic) Cell
II) Electrolytic Cell
Define Voltaic (Galvanic) Cell
Electrochemical Cell that produces electrical current from a spontaneous chemical reaction
In Voltaic Cells, the _________ does work on the ___________ and creating ___________ is the desired outcome
System; surroundings; electricity
Define Electrolytic Cell
Electrochemical Cell that consumes electrical current to drive a nonspontaneous chemical reaction
In Electrolytic Cells, the _________ does work on the ___________ and creating ___________ is the desired outcome
Surroundings; system; chemical reactions
Define Cell Potential
The driving force (difference in potential energy) that pushes electrons away from the anode and pulls them toward the cathode
The __________ the Cell Potential, the ___________ the tendency of the redox reaction to occur spontaneously
Higher; greater
What does a negative Cell Potential indicate?
Indicates forward reaction is nonspontaneous
When cells are connected, electrons flow from electrode with more ____________ charge to more ____________ charge
Negative (greater potential energy); positive (less potential energy)
What are the components of a Voltaic (Galvanic) Cell?
2 half cells, 2 electrodes, 2 aqueous electrolyte solutions, wire connecting the electrodes and 1 salt bridge
Define Electrode
Conductive surfaces through which electrons can enter or leave the half cells
Define Anode
Electrode where OXIDATION occurs
Define Cathode
Electrode where REDUCTION occurs
T/F Electrons will flow from Cathode to Anode
False; Anode to Cathode
Define Half Cell
One half of an Electrochemical Cell where either oxidation or reduction occurs
Each Half Cell contains a conductive __________ and a surrounding conductive ____________
Electrode; electrolyte
Define Electrolyte
Substance that dissolves in water to form solutions that conduct electricity
Define Salt Bridge
U-shaped tube containing a strong electrolyte to complete the circuit by flowing ions to neutralize the charge buildup in the Half Cells
Identify and label the following in this Electrochemical Cell Notation…
Anode | Electrolyte || Electrolyte | Cathode
I) Identify what the single lines represent
II) Identify what the double lines represent
III) Identify the Oxidation half and Reduction half
I) Different phases
II) Salt bridge
III) Oxidation first half (anode), Reduction second half (cathode)
What does an Electrochemical Cell Notation look like when comparing reactants/products that are in different phases?
Ex. Anode | Electrolyte || Electrolyte | Cathode
What does an Electrochemical Cell Notation look like when comparing reactants/products that are in the same phase?
Ex. Fe (s) | Fe2+ (aq) || MnO4- (aq), H+, Mn2+ (aq) | Pt (s)
Identify and label the following in this Electrochemical Cell Notation…
Fe (s) | Fe2+ (aq) || MnO4- (aq), H+, Mn2+ (aq) | Pt(s)
I) Identify what Fe (s) represents
II) Identify what the single lines represent
III) Identify what the comma represents
IV) Identify what Pt (s) represents
I) Electrode
II) Different phases
III) Same phases
IV) Inert electrode
Electrons travel from ________ to _________
Anode; Cathode
We define E^o Cell as difference in voltage between final State (________) and initial state (_________)
Cathode; Anode
E^o Cell > 0 is spontaneous or nonspontaneous, as well as what type of cell?
Spontaneous; Voltaic Cell
E^o Cell < 0 is spontaneous or nonspontaneous, as well as what type of cell?
Nonspontaneous; Electrolytic Cell
Define Standard Cell Potential (E^o Cell)
Cell potential at standard conditions
Cathode is an electrode with _______ positive E^o and has greater tendency to undergo ___________
More; reduction
Anode is an electrode with ________ positive E^o and has greater tendency to undergo ___________
Less; oxidation
More positive E^o is easier for __________, greater _________ to electrons and stronger ___________ agent
Reduction; attraction; oxidizing
Less positive E^o is easier for ___________, greater _________ to electrons and stronger ___________ agent
Oxidation; repulsion; reducing
Define Standard Hydrogen Electrode (SHE)
This electrode has an arbitrary of 0.00 V which serves as a reference potential for all other half-cell reactions
What does ΔG^o, E^o cell and K have to be to be considered spontaneous?
ΔG^o < 0
E^o cell > 0
K > 1
What does ΔG^o, E^o cell and K have to be to be considered nonspontaneous?
ΔG^o > 0
E^o cell <0
K < 1
What is the equation used to compare Cell Potential (E^o Cell) and Free Energy (ΔG^o)?
ΔG^o = -nF E^o cell
What does “F” represent in the equation used to compare Cell Potential and Free Energy?
ΔG^o = -nF E^o cell
Faraday’s constant (96485 C/mol e-)
What are the 2 equations used to compare Cell Potential (E^o Cell) and K? (At standard conditions and at given conditions)
Given conditions: E^o cell = RT/nF (lnK)
Standard conditions: E^o cell = 0.0592V/n (logK)
What is the equation used for Cell Potential at nonstandard conditions?
Nernst Equation
Given conditions: Ecell = E^o cell - RT/nF (lnQ)
Standard conditions: Ecell = E^o cell - 0.0592V/n (logQ)
Define Electrolysis
The process by which electrical current is used to drive a nonspontaneous reaction
Define Electrolytic Cell
An electrochemical cell that uses external electrical current to drive a nonspontaneous reaction
Cations are __________ at the Cathode
Reduced
Anions are ___________ at the Anode
Oxidized
____________(Cathode) with more _________ electrode potential occurs first
Reduction; positive
____________(Anode) with more ___________ electrode potential occurs first
Oxidation; negative
