Chapter 12: Electrochemistry (6%)

electrochemical cell

contained systems in which redox reactions take place

electrodes

strips of metal or other conductive materials where oxidation and reduction take place that are placed in an electrolyte solution within an electrochemical cell; comes in two types

anode, cathode

the 2 types of electrodes

anode

the electrode that is always the site of oxidation; it attracts anions

cathode

the electrode that is always the site of reduction; it attracts cations

electromotive force (emf)

the voltage or electrical potential difference of the cell

anode, cathode

electrons flow from the ________ to the ________

cathode, anode

current flows from the ________ to the ________

anode, cathode, solution, phase, salt bridge

Cell diagrams are shorthand notation that represent the reactions taking place in an electrochemical cell. They are written from _______ to ________ with electrolytes (the _________) in between. A single vertical line represents a ______ boundary while a double vertical line represents a _____ ________ or other physical boundary

Zn (s)

Zn (s) | Zn²⁺ (1 M) || Cu²⁺ (1 M) | Cu (s)

Which item in this cell diagram represents the anode?

Zn^2+

Zn (s) | Zn²⁺ (1 M) || Cu²⁺ (1 M) | Cu (s)

Which item in this cell diagram represents the anode solution (concentration)?

Cu^2+

Zn (s) | Zn²⁺ (1 M) || Cu²⁺ (1 M) | Cu (s)

Which item in this cell diagram represents the cathode solution (concentration)?

Cu (s)

Zn (s) | Zn²⁺ (1 M) || Cu²⁺ (1 M) | Cu (s)

Which item in this cell diagram represents the cathode?

galvanic (aka voltaic cells)

Galvanic vs. Electrolytic Cell

house spontaneous reactions (ΔG < 0)

galvanic (aka voltaic cells)

Galvanic vs. Electrolytic Cell

example: household nonrechargeable batteries

electrolytic (uses electrolysis)

Galvanic vs. Electrolytic Cell

houses redox reactions driven by an external voltage source

galvanic (aka voltaic cells)

Galvanic vs. Electrolytic Cell

have a positive electromotive force (emf)

electrolytic

Galvanic vs. Electrolytic Cell

house nonspontaneous reactions (ΔG > 0)

electrolytic

Galvanic vs. Electrolytic Cell

have a negative electromotive force (emf)

concentration cells

a specialized form of galvanic cell in which both electrodes are made of the same material

concentration gradient

In concentration cells, rather than a potential difference causing the movement of charge, it is the _______________ ___________ between the two solutions

galvanic (voltaic)

Galvanic vs. Electrolytic Cell

anode is negatively charged and cathode is positively charged

electrolytic

Galvanic vs. Electrolytic Cell

anode is positively charged and cathode is negatively charged

rechargeable batteries

electrochemical cells that can function as both a galvanic and electrolytic cell

energy density

the amount of energy a cell can produce relative to the mass of battery material; how rechargeable batteries are often ranked

lead-acid, NiCd, NiMH

Rank the 3 rechargeable battery examples in order from lowest to highest energy density

• Ni-Cd (Nickel-Cadmium), NiMH (Nickel-Metal Hydride), Lead-Acid

reduction potential (E_red)

tells us how likely a compound is going to be reduced

more

the higher the reduction potential, the ______ a given species wants to be reduced

0 V

the standard reduction potential (E°_red) of the standard hydrogen electrode

standard electromotive force (E°_cell)

the difference in standard reduction potential (E°_red) between the two half-cells

standard reduction potential of cathode - standard reduction potential of anode

(E°_red,cathode - E°_red,anode)

write out the formula for calculating the standard electromotive force of a cell (E°_cell = ?)

galvanic (voltaic)

Galvanic vs. Electrolytic Cell

the difference of the reduction potentials of the two half-reactions is positive

electrolytic

Galvanic vs. Electrolytic Cell

the difference of the reduction potentials of the two half-reactions is negative

opposite

electromotive force and change in free energy always have the _________ signs

-nFE°_cell

(-number of moles of electrons exchanged x Faraday constant x standard emf of the cell)

write out the formula for the standard change in free energy from standard emf (ΔG° = ?)

negative (spontaneous), galvanic (voltaic)

When E°_cell is positive, ΔG is…?

What electrochemical cell does this refer to?

positive (nonspontaneous), electrolytic

When E°_cell is negative, ΔG is…?

What electrochemical cell does this refer to?

0, concentration

When E°_cell is 0, ΔG is…?

What electrochemical cell does this refer to?

concentration, electromotive force

The Nernst equation describes the relationship between the ______________ of a species in solution under nonstandard conditions and the ______________ _______

E°_cell - (0.0592/n) x logQ

(standard emf of the cell - (0.0592/number of moles of electrons) x log(reaction quotient))

write out the formula for the Nernst equation (E_cell = ?)

positive

When K_eq is > 1, E°_cell is…?

negative

When K_eq is < 1, E°_cell is…?

0

When K_eq is = 1, E°_cell is…?