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MCAT general Chem > Elecctrochemistry > Flashcards

Elecctrochemistry Flashcards

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1
Q

Electrochemical cells

A

Contained systems where oxidation-reduction reactions occur

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2
Q

Galvanic/Voltaic cells house what kind of reaction?

A

Spontaneous

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3
Q

Electrolytic cells house what kind of reaction?

A

Nonspontaneous

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4
Q

Electromotive force (emf)

A

Voltage or electrical potential difference of the cell

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5
Q

If emf is positive

A

The reaction is spontaneous

Delta G<0

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6
Q

If emf is negative

A

The reaction is nonspontaneous

Delta G>0

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7
Q

Half cells

A

Two electrodes placed in separate compartments

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8
Q

Salt bridge

A

Made of inert salt - permits exchange of cations and anions so that the excessive charge won’t accumulate on both sides

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9
Q

Rules of a cell diagram

A
  1. )Reactants and products are always listed left to right in anode, anode soln, cathode soln, cathode
  2. ) Single vertical line means phase boundary
  3. )Double vertical is the presence of a salt bridge
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10
Q

How does the current flow?

A

From cathode to anode

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11
Q

Electrolysis

A

Oxidation-reduction drivedn by external voltage source where chemicals are decomposed

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12
Q

Electrodesposition equation

A

molM=It/nF

n=oxidation state of the compound needed

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13
Q

Concentration cell

A

A galvanic cell that ahs two half-cells connected by a conductive material, allowing spontaneous oxidation-reduction to proceed
Chemically identical electrodes

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14
Q

Rechargable cell/battery

A

Functions as both a galvanic cell and electrolytic cell

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15
Q

Lead-acid battery/lead storage battery

A 
Rechargeable battery
Voltaic/Galvanic cell- two half-cells 
Pb anode and PbO2 cathode connected by H2SO4
When fully charged-
Two PbSO4 with dilute H2SO4
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16
Q

What happens when a lead-acid battery is charging?

A

It is part of a electrolytic circuit and equations change directions

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17
Q

Energy density

A

Measure of a battery’s ability to produce power as a function of its weight

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18
Q

What is the energy density of lead-acid batteries compared to others ?

A

Low

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19
Q

Anode in lead-acid batteries?

A

Pb

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20
Q

Cathode in lead-acid batteries?

A

PbO2

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21
Q

Anode in nickel-cadmium batteries?

A

Solid cadmium

22
Q

Cathode in nickel-cadmium batteries?

A

Nickel (III) oxide-hydroxide

23
Q

What has a higher energy density, nickel-cadmium batteries or lead-acid?

A

Nickel cadium

24
Q

Surge current

A

Peridos of large current early in the discharge cycle

25
Q

Anodes considered what charge in galvanic cell?

A

Negative (low electron potential)

26
Q

Cathode considered what charge in galvanic cell?

A

Positive (high electron potential)

27
Q

What way does current flow in the anode-cathode galvanic cell?

A

From Cathode to anode

28
Q

Anode considered what charge in electrolytic cell?

A

Positive

29
Q

Cathode of electrolytic cell is what charge in electrolytic cell?

A

Negative

30
Q

Which way do anions always flow?

A

To anode

31
Q

Which way do cations always flow?

A

To cathode

32
Q

Where do reduction and oxidation always take place?

A

Anode=oxidation

Cathode=reduction

33
Q

Which way do electrons always flow?

A

From anode to cathode?

34
Q

Which way does current always flow?

A

Cathode to anode

35
Q

Reduction potential

A

Measured in volts compared relative to the standard hydrogen electrode (SHE) which has a potential of 0 V

36
Q

Reduction potential

A

Defined as the tendancy of a species to gain electrons and be reduced

37
Q

More positive potential means?

A

Greater tendency to be reduced

38
Q

Standard reduction potential (E(red))

A

Measured under standard conditions
25 degrees C
1 atm
1 M

39
Q

In galvanic cells, because electrons flow from anode (less positive) to cathode (more positive=wants to be reduced):

A

Reaction is spontaneous and Delta G is negative

40
Q

In electrolytic cells, electrode with more positive reduction potential is forced to be oxidized, so it is the:

A

Anode

41
Q

In electrolytic cells, electrode with less positive reduction potential is forced to be reduced and it is the?

A

Cathode

42
Q

What is the Delta G of the electrolytic cell?

A

Positive, non-spontaneous

Negative Ecell value

43
Q

How to get oxidation potential from reduction potential?

A

Reverse the sign

44
Q

Standard electromotive force (emf)

A

E(cell)=E(red,cathode)- E(red, anode)

45
Q

What is the Delta G of galvanic cell?

A 
Negative Delta G
Positive E(cell) values
46
Q

What species are included in the reaction quotient

A

The ones in solution

47
Q

If equilibrium constant for the reaction is between 0 and 1

A

E(cell) will be negative because ln between 0 to 1 is negative
Electrolytic cell, +G, nonspontanteous

48
Q

If equilibrium constant is greater than 1

A

E (cell) will be positive because ln greater than 1 is positive
Galvanic cell, -G, spontaneous

49
Q

What does a positive Keq mean?

A

Equilibrium lies far right

50
Q

What charge is reduced in electrolytic cells?

A

More positive reduction potential means it will be oxidized at the anode

MCAT general Chem (9 decks)

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