7. Basics of Electrochemistry

Question 1

❓ What does the law of conservation of energy state?

Answer 1

✅ Energy cannot be created or destroyed, only transformed.

Question 2

❓ How does the first law of thermodynamics relate to energy conservation?

Answer 2

✅ It states that internal energy, work, and heat convert into one another while preserving the total energy of the system.

Question 3

❓ What are electrochemical reactions?

Answer 3

✅ Reactions that involve the interconversion of electrical and chemical energy, often using redox (oxidation-reduction) reactions.

Question 4

❓ How is energy “captured” in redox reactions?

Answer 4

✅ Electrons flow from the reduced compound to the oxidized compound, and this energy can be used for engineering applications.

Question 5

❓ What is electric potential energy in chemistry?

Answer 5

✅ The ability of chemical compounds to produce electron flow, similar to gravitational potential energy.

Question 6

❓ What is oxidation?

Answer 6

✅ A process where an element loses electrons and increases its oxidation number.

Question 7

❓ What is reduction?

Answer 7

✅ A process where an element gains electrons and decreases its oxidation number.

Question 8

❓ What is a redox reaction?

Answer 8

✅ A reaction where one substance loses electrons (oxidized) while another gains electrons (reduced).

Question 9

❓ How can oxidation and reduction be identified in a reaction?

Answer 9

✅ By checking oxidation numbers:

Increase in oxidation number → Oxidation
Decrease in oxidation number → Reduction

Question 10

❓ What is an oxidation number?

Answer 10

✅ A hypothetical charge assigned to an atom based on electron transfer assumptions.

Question 11

❓ How do oxidation numbers help identify redox reactions?

Answer 11

✅ A change in oxidation number indicates oxidation or reduction.

Question 12

❓ What are key oxidation number rules?

Answer 12

✅1. Neutral molecules → Sum of oxidation numbers = 0
2. Ions → Sum of oxidation numbers = ion’s charge
3. Pure elements (e.g., O₂, N₂) → Oxidation number = 0
4. Oxygen → Usually -2, except in peroxides
5. Hydrogen → +1, except in metal hydrides (-1)

Question 13

❓ What are the main types of redox reactions?

Answer 13

✅1. Combination reactions – Two elements combine; one is oxidized, the other reduced.
2. Decomposition reactions – A compound breaks into simpler substances.
3. Displacement reactions – One element replaces another in a compound.
4. Combustion reactions – A substance reacts with oxygen, producing CO₂ or CO.
5. Disproportionation reactions – A single element undergoes both oxidation and reduction.
6. Biological redox reactions – Redox reactions essential for metabolic energy production.

Question 14

❓ What is a combustion reaction?

Answer 14

✅ A reaction where a substance burns in oxygen, producing CO₂ and H₂O (complete combustion) or CO (incomplete combustion).

Question 15

❓ What is a disproportionation reaction?

Answer 15

✅ A reaction where one element is both oxidized and reduced.

Question 16

❓ Why is balancing redox reactions more complex than regular reactions?

Answer 16

✅ Because electrons must be balanced along with elements.

Question 17

❓ What method is used to balance redox reactions?

Answer 17

✅ The half-reaction method, which follows these steps:

1. Identify oxidation and reduction half-reactions.
2. Balance elements (except O and H).
3. Balance oxygen using H₂O.
4. Balance hydrogen using H⁺ ions.
5. Balance charge using electrons.
6. Multiply reactions to equalize electrons.
7. Combine the half-reactions and verify balance.

Question 18

❓ What is a galvanic cell?

Answer 18

✅ A device that captures electron flow from a redox reaction to generate electricity.

Question 19

❓ What role do zinc sulfate (ZnSO₄) and copper sulfate (CuSO₄) play in a galvanic cell?

Answer 19

✅ They provide the electrodes and ions needed for oxidation and reduction reactions.

Question 20

❓ Why can the redox reaction occur without direct contact between solutions?

Answer 20

✅ Because oxidation occurs at the anode and reduction at the cathode, with electrons flowing through an external circuit.

Question 21

❓ What is the anode in a galvanic cell?

Answer 21

✅ The negative electrode where oxidation occurs.

Question 22

❓ What is the cathode in a galvanic cell?

Answer 22

✅ The positive electrode where reduction occurs.

Question 23

❓ How do electrons move in a galvanic cell?

Answer 23

✅ Electrons flow from the anode to the cathode via an external circuit.

Question 24

❓ Why is a salt bridge needed in a galvanic cell?

Answer 24

✅ To prevent charge buildup by allowing ion flow, maintaining electrical neutrality.

Question 25

❓ What is electromotive force (EMF)?

Answer 25

✅ The voltage (electrical potential) that drives electrons from anode to cathode.

Question 26

❓ What does standard reduction potential (SRP) measure?

Answer 26

✅ It indicates how strongly an element gains electrons (reduces) under standard conditions.

Question 27

❓ What are the standard conditions for measuring reduction potential?

Answer 27

✅1 M concentration of ions 1 atm pressure for gases 25°C temperature

Question 28

❓ How is standard EMF (E°) calculated for a reaction?

Answer 28

✅ By subtracting the standard reduction potentials: 𝐸°cell = 𝐸°cathode − 𝐸°anode ​

Question 29

❓ What happens if a half-reaction is reversed?

Answer 29

✅ The sign of the EMF value must be reversed.

Question 30

❓ What does the Nernst equation calculate?

Answer 30

✅ The voltage (EMF) of a cell under non-standard conditions.

Question 31

❓ What is the general form of the Nernst equation?

Answer 31

✅ 𝐸 = 𝐸∘ − 0.0592/𝑛 log⁡𝑄 Where: E° = Standard EMF n = Number of electrons transferred Q = Reaction quotient (ratio of concentrations)

Question 32

❓ When does the Nernst equation apply?

Answer 32

✅ Only when temperature is 25°C; adjustments are needed for other temperatures.

Question 33

❓ What is a galvanic cell, and how is it related to batteries?

Answer 33

✅ A galvanic cell consists of two half-reactions (oxidation and reduction) connected by an electrolyte, forming the basis of commercial batteries.

Question 34

❓ What were the main challenges in developing commercial batteries?

Answer 34

✅ Preventing liquid leakage, increasing voltage, durability, and efficiency, and reducing cost, weight, and toxicity.

Question 35

❓ What are modern challenges in battery development?

Answer 35

✅ Using eco-friendly materials, improving recyclability, and extending battery lifespan.

Question 36

❓ What are the two main types of batteries?

Answer 36

✅1. Non-rechargeable batteries (e.g., dry cell, alkaline batteries) 2. Rechargeable batteries (accumulators) (e.g., lithium-ion, lead-acid batteries)

Question 37

❓ What are dry cell batteries, and where are they commonly used?

Answer 37

✅ Non-rechargeable batteries used in remotes, toys, and portable electronics.

Question 38

❓ What is the chemistry behind dry cell batteries?

Answer 38

✅ Based on the Leclanché cell, originally containing ammonium chloride (NH₄Cl) solution, later replaced by an acidic electrolyte paste.

Question 39

❓ What is the difference between Leclanché cells and alkaline batteries?

Answer 39

✅ Alkaline batteries use potassium hydroxide (KOH) as the electrolyte instead of acidic paste.

Question 40

❓ Why are lithium-ion (Li-ion) batteries popular?

Answer 40

✅ They offer high efficiency, long lifespan, low weight, and rechargeability.

Question 41

❓ What determines the cathode reaction in a lithium-ion battery?

Answer 41

✅ The cathode material, which varies by manufacturer and application. Common materials include: Lithium-cobalt oxide (LiCoO₂) Lithium-iron phosphate (LiFePO₄) Lithium-manganese oxide (LiMn₂O₄) Lithium-nickel manganese cobalt oxide (NMCO)

Question 42

❓ How does a lithium-ion battery charge and discharge?

Answer 42

✅Discharge mode: Electrons flow from anode (oxidation) to cathode (reduction). Charge mode: Electrons flow in reverse, moving Li⁺ ions back to the anode.

Question 43

❓ Why do the anode and cathode switch roles in Li-ion batteries?

Answer 43

✅ By definition, oxidation always occurs at the anode. During charging, oxidation happens at the cathode, so the electrodes technically switch roles.

Question 44

❓ Where are lead-acid batteries commonly used?

Answer 44

✅ Motor vehicles and backup power systems due to their low cost and reliability.

Question 45

❓ How do lead-acid batteries work?

Answer 45

✅ Anode reaction (oxidation): Lead (Pb) is oxidized to lead sulfate (PbSO₄). Cathode reaction (reduction): Lead dioxide (PbO₂) is reduced to lead sulfate (PbSO₄). Electrolyte: Sulfuric acid (H₂SO₄) allows ion flow to maintain charge balance.

Question 46

❓ Why are lead-acid batteries still in use despite newer technologies?

Answer 46

✅ They are cheaper and well-established, making them cost-effective for many applications.

Question 47

❓ How do fuel cells differ from batteries?

Answer 47

✅ Unlike batteries, fuel cells work continuously by supplying reducing and oxidizing agents externally, whereas batteries operate in cycles (charging and discharging).

Question 48

❓ What do fuel cells and batteries have in common?

Answer 48

✅ Both have an anode, cathode, and electrolyte, where electrons flow from anode to cathode, generating electricity.

Question 49

❓ How do fuel cells generate electricity?

Answer 49

✅ Fuel cells produce electricity by continuously reacting hydrogen (H₂) with oxygen (O₂) to form water (H₂O) in a controlled, exothermic reaction.

Question 50

❓ What historical disaster is linked to the hydrogen-oxygen reaction?

Answer 50

✅ The Hindenburg disaster, where hydrogen reacted explosively with oxygen.

Question 51

❓ What are the main ways fuel cells are classified?

Answer 51

✅ Fuel cells can be classified by: 1. Electrolyte type (e.g., proton exchange membrane, alkaline, molten carbonate, solid oxide, phosphoric acid). 2. Fuel or agent type (most use hydrogen & oxygen, but others exist, like propane-oxygen). 3. Operating temperature (High-Temperature > 600°C, Low-Temperature < 600°C). 4. Efficiency (varies based on design, temperature, and application). 5. Application (e.g., mobile, stationary, spaceflight, public transport, military, Mars rovers). 6. Electrode or catalyst material (e.g., precious metals like platinum, or cheaper metals like iron, cobalt, nickel).

Question 52

❓ What is a Proton Exchange Membrane Fuel Cell (PEMFC)?

Answer 52

✅ A fuel cell that uses a polymer membrane as an electrolyte, allowing ion flow while preventing electrical conductivity.

Question 53

❓ Where are PEMFCs used?

Answer 53

✅ Used in mobile and stationary applications (e.g., vehicles, backup power).

Question 54

❓ How are PEM fuel cells categorized?

Answer 54

✅ Low-Temperature PEM (LT PEM): Operates below 100°C, requires high-purity hydrogen (CO contamination reduces efficiency). High-Temperature PEM (HT PEM): Operates between 120-200°C, more tolerant to carbon monoxide impurities.

Question 55

❓ What is a major weakness of LT PEM fuel cells?

Answer 55

✅ Carbon monoxide (CO) contamination, which can poison the membrane, requiring high-purity hydrogen.

Question 56

❓ What is an Alkaline Fuel Cell (AFC)?

Answer 56

✅ A fuel cell that uses an alkaline electrolyte (e.g., sodium or potassium hydroxide).

Question 57

❓ What is the typical operating temperature of an AFC?

Answer 57

✅ Below 100°C.

Question 58

❓ What is the efficiency range of an AFC?

Answer 58

✅ 30-80% efficiency.

Question 59

❓ What is a weakness of AFCs?

Answer 59

✅ Carbon dioxide (CO₂) reduces performance, affecting efficiency when exposed to air.

Question 60

❓ What is a recent development in AFC technology?

Answer 60

✅ Anion Exchange Membrane Fuel Cells (AEMFCs), which use a solid anion-exchange membrane instead of liquid electrolytes, improving efficiency.

Question 61

❓ What is electrolysis?

Answer 61

✅ Electrolysis is a process where electricity drives a non-spontaneous chemical reaction in an electrolytic cell.

Question 62

❓ How is an electrolytic cell similar to a fuel cell?

Answer 62

✅ It works in reverse of a fuel cell, continuously using electricity to force a reaction.

Question 63

❓ What is a common example of an electrolytic cell?

Answer 63

✅ A Downs cell, used to produce metallic sodium (Na) and chlorine (Cl₂) from sodium chloride (NaCl).

Question 64

❓ Why is electricity required for electrolysis?

Answer 64

✅ The reaction has a negative standard potential, meaning it is non-spontaneous and needs an external energy source.

Question 65

❓ What is the temperature at which a Downs cell operates?

Answer 65

✅ 801°C.

Question 66

❓ How can hydrogen be produced using electrolysis?

Answer 66

✅ By using electricity to split water (H₂O) into hydrogen (H₂) and oxygen (O₂).

Question 67

❓ How does this process relate to fuel cells?

Answer 67

✅ The electrolysis of water is the reverse reaction of a hydrogen fuel cell.

Question 68

❓ What is electroplating?

Answer 68

✅ A process that uses electrolysis to deposit a metal coating onto a surface for protection or decoration.

Question 69

❓ How does electroplating work?

Answer 69

✅ Electrons move from the anode to the cathode, causing metal ions (Mn⁺) to be reduced and form a solid metal layer on the cathode.

Question 70

❓ What is an example of an electroplating reaction?

Answer 70

✅ The reduction of copper ions (Cu²⁺) to solid copper (Cu) at the cathode.

Question 71

❓ What factors determine the exact half-reactions in electroplating?

Answer 71

✅ The electrolyte and the metal used for the coating.

Question 72

❓ What is corrosion?

Answer 72

✅ The spontaneous oxidation of a metal surface, causing degradation over time.

Question 73

❓ How does corrosion occur?

Answer 73

✅ The metal acts as an anode, where oxidation occurs, while oxygen is reduced to form water.

Question 74

❓ How does corrosion relate to electroplating?

Answer 74

✅ Corrosion is the reverse of electroplating, where instead of depositing metal, the metal surface oxidizes and deteriorates.

Question 75

❓ What constant is used to calculate the amount of metal deposited in electroplating?

Answer 75

✅ The Faraday constant (F).

Question 76

❓ What formula determines the amount of metal deposited?

Answer 76

✅ (𝐼×𝑡)/(𝐹×𝑛) ​ where: I = Current (Amperes) t = Time (Seconds) F = Faraday constant n = Number of electrons needed for reduction

Question 77

❓ How can you calculate the total weight of deposited metal?

Answer 77

✅ Multiply the moles of metal by its atomic weight.

Question 78

❓ What are the units of the final deposited metal calculation?

Answer 78

✅ Grams (g).