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MCAT Chem > Electrochemistry > Flashcards

Electrochemistry Flashcards

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1
Q

electrochemical cells

A

contained systems in which redox rxns occur

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2
Q

3 types of electrochem cells

A

1) galvanic
2) electrolytic cells
3) concentration cells

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3
Q

all three types of the electrochemical cells contain…

A

electrodes where oxidation and reduction take place

oxidation electrode called anode

reduction electrode called cathode

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4
Q

emf positive

A

ΔG < 0 spontaneous cell can release energy

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5
Q

emf negative

A

ΔG > 0 nonspontaneous cell will absorb energy

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6
Q

for all electrochemical cells, electrons move…

A

from anode to cathode

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7
Q

for all electrochemical cells, current (I) runs…

A

from cathode to anode

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8
Q

galvanic cells

A

house spontaneous rxns
non-rechargeable batteries
cell release energy into environment
emf Ecell is positive

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9
Q

emf and free energy change…

A

must always have opposite signs

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10
Q

electrodes of galvanic cells

A
  • half- cells
  • connected by conductive material usually copper wire
  • surrounded by electrolyte soln w cations and anions
  • connected by salt bridge that consists of an inert salt (charge gradient)
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11
Q

cell diagram

A

Zn(s)|Zn2+(1M) || Cu2+(1M)|Cu(s)
an-anode soln-cathode soln-cath

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12
Q

electrolytic cells

A
  • houses nonspontaneous rxns
  • reduction at cathode, ox at anode
  • require energy input to proceed
  • driven by external voltage source (chemical compounds decomposed)
  • isolate elements
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13
Q

Faraday constant

A

10^5

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14
Q

electrodeposition equation

A

mol M = It/nF

M: moles of metal ion at a particular electrode
I: current
t: time
n: # of e- equivalents
F: Faraday constant

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15
Q

concentration cell

A
  • 2 half cells for the spontaneous redox rxns
  • electrodes chemically identical
  • concentration gradient results in potential difference between the two compartments and drives the movement of electrons in the direction that results in equilibrium of the ion-gradient
  • current will stop when the concentrations of ionic species in the half-cells are equal
  • V/emf is 0 when concentrations are equal
  • Voltage calculated using Nernst equation
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16
Q

rechargeable cell…

A

can function as both a galvanic and electrolytic cell

17
Q

lead-acid battery

A
  • as a voltaic cell, when fully charged, 2 half cells: Pb anode and PbO2 cathode and connected by 4M H2SO4 conductive material

when fully discharged consists of 2 PbSO4 electroplated lead electrodes with a dilute concentration of H2SO4

  • dilute acid electrolyte when discharging
  • when charging the lead-acid cell is part of an electrolytic circuit
  • low energy-to-weight ratio
18
Q

nickel-cadmium batteries

A
  • rechargeable battery
  • 2 half cells solid cadmium anode and nickel(III) oxide-hydroxide cathode connected by conductive material typically KOH
  • Ni(OH)2 and Cd(OH)2 products
  • surge currents: periods of large current early in the discharge cycle
  • Ni-Cd half rxns tend to provide higher surge current
19
Q

in galvanic cells electrons move from…

A

neg (low EP) to pos (high EP)

20
Q

anode of electrolytic cell is…

A

positive

21
Q

cathode ALWAYS attracts ______ regardless of charge

A

cations

22
Q

oxidation ALWAYS takes place ______

A

at the anode

23
Q

reductions ALWAYS takes place _______

A

at the cathode

24
Q

anode ALWAYS attracts ________

A

anions

25
Q

a positive E°red indicates…

A

spontaneous reduction

26
Q

why is the ΔG of the electrolytic cells positive?

A

anode has pos reduction potential and cathode has negative, so an external voltage source must force the appropriate rxns in the appropriate places

27
Q

standard electrochemical force of a cell

A

E°cell = E°red,cath - E°red,an

28
Q

standard change in free energy from standard emf

A

ΔG° = -nFE°cell

29
Q

Nernst eq

A

Ecell = E°cell - (0.0592/n • logQ)

or (RT/nF • lnQ)

30
Q

rxn quotient

A

Q = [C]^c•[D]^d / [A]^a•[B]^b

31
Q

standard change in free energy from eq constant

A

ΔG° = -RTlnKeq

32
Q

free energy change nonstandard

A

ΔG = ΔG° + RTlnQ

33
Q

in galvanic cells, species with the more ________ is reduced whereas in electrolytic the opposite is true.

A

more positive reduction potential

MCAT Chem (13 decks)

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