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C.Chem 3+14- Redox 1+2 > Electrochemistry > Flashcards

Electrochemistry Flashcards

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1
Q

Why can a high resistance voltmeter be used in electrochemical cells but not in a battery

A

In electrochemical cells = No current allows max potential difference to be measured between half cells

In a battery = purpose is to create current from potential difference = High Resistance would prevent this = battery would run out as reactants at electrodes used up

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2
Q

How is E•cell linked to Gibbs free energy + entropy

A

E•cell is directly proportional to entropy, equilibrium constant(k or LnK) and gibbs free energy

G = AH - (AS x T)
= larger entropy the more negative G

G = -R(gas constant) x T x LnK
= large Kc value = greater proportion of products to reactants at equilibrium
Higher Kc = more negative G = more feasible

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3
Q

What do delta G, Kc ,Entropy(total) and E•cell all give information on

A

Feasibility of a reaction

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4
Q

What are the limitations of predicting a reaction to be feasible just off a positive E•cell

A

1- activation energy may be very high

2- conditions may not be at standard conditions = by changing conditions a reaction can be feasible eg: raising the temp

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5
Q

How could decreasing the concentration of Mg2+ in this reaction affect the E•cell and equilibrium

Mg2+ + 2e- = Mg E•cell = -2.73v

A

If Mg2+ conc decreases = equilibrium moves to left = more electrons released = electrode becomes more negative = E•cell is more negative

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6
Q

How do fuel cells create a voltage

A

Reaction of hydrogen rich fuels + oxygen

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7
Q

Give 2 advantages of the use of methanol as a fuel

A

Less CO2 produced compared to fossil fuels

CH3OH is a renewable biofuel

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8
Q

Give 2 disadvantages of using hydrogen fuel cells

A

H2 is difficult to transport + store

No Hydrogen infrastructure currently

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9
Q

What is an advantage of hydrogen fuel cell

A

Don’t need to be recharged = work until fuel runs out

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10
Q

What electrodes are used in hydrogen fuel cell

A

Platinum

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11
Q

What does the high resistance voltmeter measure and how

A

Measures voltage = how hard the electrons are being pushed
- the high resistance stops electrons flowing to measure how hard there being pushed

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12
Q

What is a battery

A

Multiple electrical cells

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13
Q

What is the overall equation of a hydrogen fuel cell

A

1/2 O2 + H2O + H2 + 2OH- = 2OH- + 2H20
Cancels out to =

1/2 O2 + H2 = H2O

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14
Q

What happens in a hydrogen oxygen fuel cell

A

H2 gas flows in one side + Oxygen gas flows in the other = they both react + WATER flows out

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15
Q

What are hydrogen fuel cells only bi-product

A

Water

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16
Q

What is in the acidic electrolyte for hydrogen fuel cell

A

H+ ions

17
Q

What is in the alkaline electrolyte for hydrogen fuel cell

A

OH-

18
Q

What does the electrolyte do in a hydrogen fuel cell

A

Electrolyte remains in fuel cell + facilitates/controls flow of either H+ or OH- and electrons between the 2 sides/electrodes for reaction to occor

19
Q

What is the main disadvantage of hydrogen fuel cell

A

Need energy to build the fuel cells + to produce the hydrogen fuel itself = this takes energy + comes from fossil fuels

20
Q

What does a usual cell notation look like

A

Reduced form|Oxidised form||oxidised form | reduced form

= most positive values go in centre

21
Q

What does a solid single line represent in cell notation

A

Physical state change
Eg Zn(s)| Zn2+(aq)

22
Q

What does a comma represent in cell notation

A

Same physical state
Eg Fe3+(aq), Fe2+

23
Q

Write the half equation of oxygen in hydrogen fuel cell in acidic conditions

A

1/2 O2 + 2H+ + 2e- = H2O

24
Q

Write the half equation of hydrogen in hydrogen fuel cell in alkaline conditions

A

H2 + 2OH- = 2H2O + 2e-

25
Q

How can you recharge a battery

A

Applying a potential difference in the opposite direction regenerates the chemicals

26
Q

In a hydrogen fuel cell which electrode is negative

A

Hydrogen = negative electrode

Oxygen = positive electrode

A positive electrode means it’s reduced (as less electrons in solution)

27
Q

In a Lithium Cobalt battery what are the 2 electrodes made of

A

LiCoO2 = Lithium cobalt

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C.Chem 3+14- Redox 1+2 (3 decks)

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