Chapter 4: 4.2 Voltaic Cells Flashcards
Define:
Electrochemistry
The branch of chemistry that studies this interconversion of chemical and electrical energy
Define:
Electrochemical cells
The experimental setup that produces or uses an electric current and does or converts electrical work through the use of a redox reaction
Define:
Galvanic cells/Voltaic cell
Electrochemical cells that produce current
Define:
Electrolysis
The process if a chemical reaction is forced to occur in an electrochemical cell by introducing an electric current from an external source
Define:
Electrolytic cell
When the experimental setup,
Define:
Half-cell
The physically separated subsystem where each half reaction occurs
Where in each half-cell do the half-reactions take place?
On the surfaces of an electrode
Define:
Electrode
An electronic conductor (usually a metal or graphite bar) that is in contact with an ionic conductor or electrolyte
What is usually used as an electrolyte?
A solution or a molten salt
How was the battery built by Volta?
Used a stacked pile of alternating zinc and copper disks separated by cloth soaked in brine and sulfuric acid
What was the successor to Volta’s battery design?
The Daniell Cell
True or False:
Reduction occurs at the cathode
True
What does oxidation occur in a electrochemical cell?
Anode
In a cell diagram:
What is written first on the left?
(Use Zn + Cu2+ → Zn2+ Cu)
The anode
* Zn
In a cell diagram:
How is are the other species written?
(Use Zn + Cu2+ → Zn2+ Cu)
Written in the order in which they occur in the cell from the anode to the cathode
* Zn, Zn2+, Cu2+, Cu
In a cell diagram:
What do vertical lines indicate?
(Use Zn + Cu2+ → Zn2+ Cu)
Phase boundaries
* Zn|Zn2+, Cu2+|Cu
In a cell diagram:
What does a double vertical bar indicate?
(Use Zn + Cu2+ → Zn2+ Cu)
The salt bridge (or equivalent)
* Zn|Zn2+||Cu2+|Cu
In a cell diagram:
What are inert electrodes? How are they indicated?
Graphite, platinum etc.
* Placed on the anode/cathode end as applicable
* Separated from the adjacent phase by single vertical bar
True or False:
Stoichiometric coefficients are shown on cell diagrams
False, the following 2 are not shown on cell diagrams:
1. Stoichiometric coefficients
2. Species that are neither reduced nor oxidized
- What is the electrical energy difference (E)?
- What is it also known as?
- How can it be measured?
- The electrical energy difference between any two electrodes in an electrochemical cell
- Cell potential or cell voltage
- Experimentally measured with a voltmeter
What is standard conditions for electrochemical cells?
1.0 M and 25°C
What is the standard potentials of electrodes measured relative to?
Standard hydrogen electrode (SHE)
True or False:
Stronger oxidizing agents have more negative E^o values
False, they have more positive E^o values
What E^o values are associated with stronger reducing agents?
Lower E^o values
List:
The steps to finding the Standard Cell Potential
- Identify the reduction half-reaction and look up its standard potential
- Identify the oxidation half-reaction and look up its standard potential
- Cell potential is the difference between the reduction half reaction potential minus oxidation half-reaction potential
True or False:
When calculating standard cell potential, we multiply the E^o values by the coefficients required to cancel electron values
False, the E^o values is NOT multiplied
How is the standard cell potential of a redox reaction related to that reaction’s standard free energy change?
ΔG^o = -nFE^o(cell)
In the reaction ΔG^o = -nFE^o(cell):
1. What does n stand for?
2. What does F stand for?
- Number of moles of electrons transferred between the electodes in the complete reaction
- Proportionality constant (Faraday constant)
What is the value of the Faraday constant?
96,485 Coulombs (C) per mole of unit charges
How can we tell if a given redox reaction will occur spontaneously as written based on the sign of the corresponding standard cell potential?
- If E^o(cell), then the reaction is spontaneous from left to right as written
- If E^o(cell), then the reverse reaction (from right to left) is spontaneous
- If E^o(cell), then the cell reaction is at equilibrium
The relationship between free energy under non-standard and standard conditions is shown by which equation?
ΔG = ΔG^o +RTlnQ
The relationship between free energy under standard and non-standard conditions using cell potentials will form a formula known as what?
Nernst Equation
State the formula for:
Nernst Equation
E(cell) = E^o(cell) - (RT/nF)lnQ
State:
The variables of the Nernst equation
E(cell) = E^o(cell) - (RT/nF)lnQ
* Q is the reaction quotient
* R is the gas constant = 8.314 J/K mol
* T is the absolute temperature in Kelvin
