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Electrochemistry Flashcards

Learn the fundamentals of electrochemistry, including the Standard Hydrogen Electrode, electrode potentials, galvanic cells, Nernst equation, and application...

24 cards~8 min
Electrochemistry Flashcards — Qwi
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1What is the assigned electrode potential of the Standard Hydrogen Electrode?
Answer

0 V

By convention, the electrode potential of SHE is assigned a value of zero (0 V). This makes it the reference point for all other electrode potentials.
2Under standard conditions, what is the pressure of hydrogen gas in the SHE?
Answer

1 atm

Standard conditions specify that the hydrogen gas pressure is 1 atmosphere (1 atm). This ensures consistent measurement of electrode potentials.
3The SHE is a half-cell where {{hydrogen gas}} is in contact with hydrogen ions.
Answer

hydrogen gas

4The standard electrode potential is defined as the potential difference between a given half-cell and the {{standard hydrogen electrode}}.
Answer

standard hydrogen electrode

5The standard electrode potential of a half-cell can be measured independently of any reference.
Answer

False

It is not possible to determine the electrode potential of a single electrode (half-cell) independently; potentials are always measured relative to SHE.
6In a galvanic cell, the electrode with the higher reduction potential acts as the anode.
Answer

False

The electrode with the higher standard reduction potential always acts as the cathode, where reduction occurs.
7Which electrode acts as cathode in a Zn/Cu cell?
Answer

Cu electrode | Zn electrode

Copper has the higher reduction potential (+0.34 V) compared to zinc (−0.76 V), so Cu is the cathode and Zn is the anode.
8Which metal is more reactive, Zn or Cu?
Answer

Zn (more negative) | Cu (less negative)

Metals with lower (more negative) reduction potentials are more reactive; Zn (−0.76 V) is more reactive than Cu (+0.34 V).
9What is the formula to calculate the standard emf of a galvanic cell?
Answer

Ecell° = Ered(cathode)° − Ered(anode)°

The standard emf is the difference between the cathode and anode reduction potentials under standard conditions.
10For the Zn/Cu cell, Ecell° = 0.34 − ({{−0.76}}) = 1.10 V.
Answer

-0.76

11A positive standard emf indicates a spontaneous galvanic cell.
Answer

True

If Ecell° > 0 the cell will operate (it is spontaneous).
12If the value of Ecell° is positive, the cell representation is correct.
Answer

True

A positive cell potential confirms that the chosen anode‑cathode order follows the electrochemical series.
13How does oxidation potential relate to reduction potential?
Answer

Oxidation potential = − reduction potential | Same magnitude, opposite sign

Oxidation potential is the negative of reduction potential; they have equal magnitude but opposite sign.
14What does a more positive standard reduction potential indicate about a species' oxidizing power?
Answer

Stronger oxidizing agent

A higher (more positive) value means the species has a greater tendency to gain electrons and hence behaves as a stronger oxidizing agent.
15Metals with lower (more {{negative}}) reduction potential are more reactive.
Answer

negative

16A metal with a more negative reduction potential can displace a metal with a more positive reduction potential from its solution.
Answer

True

A metal with lower (more negative) E° value can displace a metal with higher (more positive) E° value.
17According to the Nernst equation, what factor multiplies log Q for a half‑cell at 25 °C?
Answer

0.05912/n

The Nernst equation at 25 °C is E = E° − (0.05912/n) log Q, where n is the number of electrons transferred.
18The Nernst equation for a half‑cell at 25 °C is E = E° − 0.05912/{{n}} log Q.
Answer

n

19Which material is suitable for a container storing Cu²⁺ solution, iron or a metal with higher E°?
Answer

Metal with higher E° | Iron

The container must have a higher (more positive) potential than the solution ion; iron (−0.44 V) is lower than Cu²⁺ (+0.34 V) and thus unsuitable.
20What is the typical efficiency range of electric motors compared to internal combustion engines?
Answer

85‑95% vs 25‑35%

Electric motors achieve efficiencies of around 85‑95%, whereas petrol or diesel engines operate at only 25‑35% efficiency.
21Electric cars emit no exhaust gases while driving.
Answer

True

Electric cars produce no exhaust emission while driving, reducing air pollution in cities.
22What are the three evaluation criteria for electrochemical cells in electric cars?
Answer

Energy efficiency | Renewability | Environmental impact

Their use can be evaluated in terms of energy efficiency, renewability, and environmental impact.
23What is the standard reduction potential of the Zn²⁺/Zn couple?
Answer

–0.76 V

The standard reduction potential of the zinc electrode is –0.76 V, indicating its tendency to be reduced.
24The standard reduction potential of the Cu²⁺/Cu couple is {{+0.34 V}}.
Answer

+0.34 V

Standard Hydrogen Electrode (SHE)

The Standard Hydrogen Electrode is the universal reference for measuring electrode potentials. By convention, its assigned potential is 0 V. Under standard conditions the hydrogen gas pressure is 1 atm, and the half‑cell consists of hydrogen gas in contact with hydrogen ions (H⁺) in solution.

Why SHE is the Reference

All other electrode potentials are expressed as the potential difference between a given half‑cell and the SHE. This convention allows a consistent electrochemical series and makes it possible to compare the reducing or oxidizing power of different species.

Standard Electrode Potentials

Standard electrode potentials (E°) are measured under standard conditions (25 °C, 1 M concentrations, 1 atm gas pressure). They are always relative to the SHE; a single half‑cell cannot be measured independently of a reference.

  • True statement: The standard electrode potential is defined as the potential difference between a given half‑cell and the standard hydrogen electrode.
  • False statement: The standard electrode potential of a half‑cell can be measured independently of any reference.

Interpreting Potentials

A more positive standard reduction potential indicates a stronger oxidizing agent because the species has a greater tendency to gain electrons. Conversely, metals with more negative reduction potentials are more reactive and can displace metals with more positive potentials from solution.

Galvanic Cells

In a galvanic (voltaic) cell the spontaneous redox reaction generates an electric current. The cell potential (E°_cell) is calculated by subtracting the anode reduction potential from the cathode reduction potential:

E°_cell = E°_cathode − E°_anode

For example, in a Zn/Cu cell:

  • Cu²⁺/Cu reduction potential: +0.34 V
  • Zn²⁺/Zn reduction potential: −0.76 V

Thus, E°_cell = 0.34 V − (−0.76 V) = 1.10 V. A positive E°_cell indicates a spontaneous reaction.

Anode and Cathode Identification

The electrode with the higher reduction potential always acts as the cathode (reduction occurs there). In the Zn/Cu cell, copper is the cathode and zinc is the anode. The statement “the electrode with the higher reduction potential acts as the anode” is false.

Nernst Equation

The Nernst equation relates the actual electrode potential (E) to the standard potential (E°), temperature, and reaction quotient (Q). At 25 °C the equation for a half‑cell is:

E = E° − (0.05912/n) log Q

Here, n is the number of electrons transferred in the half‑reaction. The factor 0.05912 /n multiplies log Q.

Application Example

For a half‑cell involving the Zn²⁺/Zn couple (n = 2), the Nernst term becomes 0.02956 log [Zn²⁺]. This term adjusts the potential according to the actual ion concentration.

Practical Implications

Understanding electrode potentials is essential for selecting materials in electrochemical devices. For instance, a container storing a Cu²⁺ solution should be made of a material with a higher (more positive) E° than Cu²⁺ to avoid unwanted corrosion. Iron, with a lower potential (−0.44 V), would be unsuitable.

Electrochemical Evaluation in Electric Vehicles

When assessing electrochemical cells for electric cars, three criteria are commonly used:

  • Energy efficiency
  • Renewability of the energy source
  • Environmental impact

Electric motors themselves are highly efficient, typically achieving 85‑95 % efficiency compared to 25‑35 % for internal combustion engines. Moreover, electric cars emit no exhaust gases while driving, contributing to lower urban air pollution.

Key Takeaways

  1. The Standard Hydrogen Electrode defines the zero point for all electrode potentials (0 V, 1 atm H₂).
  2. Standard reduction potentials indicate the relative tendency of species to be reduced; more positive values mean stronger oxidizing agents.
  3. In galvanic cells, the cathode is the electrode with the higher reduction potential; the cell potential is the difference between cathode and anode potentials.
  4. The Nernst equation adjusts standard potentials for non‑standard conditions using the factor 0.05912 /n at 25 °C.
  5. Electrochemical knowledge guides material selection and performance evaluation in technologies such as electric vehicles.