7. Basics of Electrochemistry Flashcards
❓ What does the law of conservation of energy state?
✅ Energy cannot be created or destroyed, only transformed.
❓ How does the first law of thermodynamics relate to energy conservation?
✅ It states that internal energy, work, and heat convert into one another while preserving the total energy of the system.
❓ What are electrochemical reactions?
✅ Reactions that involve the interconversion of electrical and chemical energy, often using redox (oxidation-reduction) reactions.
❓ How is energy “captured” in redox reactions?
✅ Electrons flow from the reduced compound to the oxidized compound, and this energy can be used for engineering applications.
❓ What is electric potential energy in chemistry?
✅ The ability of chemical compounds to produce electron flow, similar to gravitational potential energy.
❓ What is oxidation?
✅ A process where an element loses electrons and increases its oxidation number.
❓ What is reduction?
✅ A process where an element gains electrons and decreases its oxidation number.
❓ What is a redox reaction?
✅ A reaction where one substance loses electrons (oxidized) while another gains electrons (reduced).
❓ How can oxidation and reduction be identified in a reaction?
✅ By checking oxidation numbers:
Increase in oxidation number → Oxidation
Decrease in oxidation number → Reduction
❓ What is an oxidation number?
✅ A hypothetical charge assigned to an atom based on electron transfer assumptions.
❓ How do oxidation numbers help identify redox reactions?
✅ A change in oxidation number indicates oxidation or reduction.
❓ What are key oxidation number rules?
✅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)
❓ What are the main types of redox reactions?
✅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.
❓ What is a combustion reaction?
✅ A reaction where a substance burns in oxygen, producing CO₂ and H₂O (complete combustion) or CO (incomplete combustion).
❓ What is a disproportionation reaction?
✅ A reaction where one element is both oxidized and reduced.
❓ Why is balancing redox reactions more complex than regular reactions?
✅ Because electrons must be balanced along with elements.
❓ What method is used to balance redox reactions?
✅ The half-reaction method, which follows these steps:
- Identify oxidation and reduction half-reactions.
- Balance elements (except O and H).
- Balance oxygen using H₂O.
- Balance hydrogen using H⁺ ions.
- Balance charge using electrons.
- Multiply reactions to equalize electrons.
- Combine the half-reactions and verify balance.
❓ What is a galvanic cell?
✅ A device that captures electron flow from a redox reaction to generate electricity.
❓ What role do zinc sulfate (ZnSO₄) and copper sulfate (CuSO₄) play in a galvanic cell?
✅ They provide the electrodes and ions needed for oxidation and reduction reactions.
❓ Why can the redox reaction occur without direct contact between solutions?
✅ Because oxidation occurs at the anode and reduction at the cathode, with electrons flowing through an external circuit.
❓ What is the anode in a galvanic cell?
✅ The negative electrode where oxidation occurs.
❓ What is the cathode in a galvanic cell?
✅ The positive electrode where reduction occurs.
❓ How do electrons move in a galvanic cell?
✅ Electrons flow from the anode to the cathode via an external circuit.
❓ Why is a salt bridge needed in a galvanic cell?
✅ To prevent charge buildup by allowing ion flow, maintaining electrical neutrality.
❓ What is electromotive force (EMF)?
✅ The voltage (electrical potential) that drives electrons from anode to cathode.
❓ What does standard reduction potential (SRP) measure?
✅ It indicates how strongly an element gains electrons (reduces) under standard conditions.
❓ What are the standard conditions for measuring reduction potential?
✅1 M concentration of ions
1 atm pressure for gases
25°C temperature
❓ How is standard EMF (E°) calculated for a reaction?
✅ By subtracting the standard reduction potentials:
𝐸°cell = 𝐸°cathode − 𝐸°anode
❓ What happens if a half-reaction is reversed?
✅ The sign of the EMF value must be reversed.
❓ What does the Nernst equation calculate?
✅ The voltage (EMF) of a cell under non-standard conditions.
❓ What is the general form of the Nernst equation?
✅
𝐸 = 𝐸∘ − 0.0592/𝑛 log𝑄
Where:
E° = Standard EMF
n = Number of electrons transferred
Q = Reaction quotient (ratio of concentrations)
❓ When does the Nernst equation apply?
✅ Only when temperature is 25°C; adjustments are needed for other temperatures.
❓ What is a galvanic cell, and how is it related to batteries?
✅ A galvanic cell consists of two half-reactions (oxidation and reduction) connected by an electrolyte, forming the basis of commercial batteries.
❓ What were the main challenges in developing commercial batteries?
✅ Preventing liquid leakage, increasing voltage, durability, and efficiency, and reducing cost, weight, and toxicity.
❓ What are modern challenges in battery development?
✅ Using eco-friendly materials, improving recyclability, and extending battery lifespan.
❓ What are the two main types of batteries?
✅1. Non-rechargeable batteries (e.g., dry cell, alkaline batteries)
2. Rechargeable batteries (accumulators) (e.g., lithium-ion, lead-acid batteries)
❓ What are dry cell batteries, and where are they commonly used?
✅ Non-rechargeable batteries used in remotes, toys, and portable electronics.
❓ What is the chemistry behind dry cell batteries?
✅ Based on the Leclanché cell, originally containing ammonium chloride (NH₄Cl) solution, later replaced by an acidic electrolyte paste.
❓ What is the difference between Leclanché cells and alkaline batteries?
✅ Alkaline batteries use potassium hydroxide (KOH) as the electrolyte instead of acidic paste.
❓ Why are lithium-ion (Li-ion) batteries popular?
✅ They offer high efficiency, long lifespan, low weight, and rechargeability.
❓ What determines the cathode reaction in a lithium-ion battery?
✅ 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)
❓ How does a lithium-ion battery charge and discharge?
✅Discharge mode: Electrons flow from anode (oxidation) to cathode (reduction).
Charge mode: Electrons flow in reverse, moving Li⁺ ions back to the anode.
❓ Why do the anode and cathode switch roles in Li-ion batteries?
✅ By definition, oxidation always occurs at the anode. During charging, oxidation happens at the cathode, so the electrodes technically switch roles.
❓ Where are lead-acid batteries commonly used?
✅ Motor vehicles and backup power systems due to their low cost and reliability.
❓ How do lead-acid batteries work?
✅
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.
❓ Why are lead-acid batteries still in use despite newer technologies?
✅ They are cheaper and well-established, making them cost-effective for many applications.
❓ How do fuel cells differ from batteries?
✅ Unlike batteries, fuel cells work continuously by supplying reducing and oxidizing agents externally, whereas batteries operate in cycles (charging and discharging).
❓ What do fuel cells and batteries have in common?
✅ Both have an anode, cathode, and electrolyte, where electrons flow from anode to cathode, generating electricity.
❓ How do fuel cells generate electricity?
✅ Fuel cells produce electricity by continuously reacting hydrogen (H₂) with oxygen (O₂) to form water (H₂O) in a controlled, exothermic reaction.
❓ What historical disaster is linked to the hydrogen-oxygen reaction?
✅ The Hindenburg disaster, where hydrogen reacted explosively with oxygen.
❓ What are the main ways fuel cells are classified?
✅ Fuel cells can be classified by:
- Electrolyte type (e.g., proton exchange membrane, alkaline, molten carbonate, solid oxide, phosphoric acid).
- Fuel or agent type (most use hydrogen & oxygen, but others exist, like propane-oxygen).
- Operating temperature (High-Temperature > 600°C, Low-Temperature < 600°C).
- Efficiency (varies based on design, temperature, and application).
- Application (e.g., mobile, stationary, spaceflight, public transport, military, Mars rovers).
- Electrode or catalyst material (e.g., precious metals like platinum, or cheaper metals like iron, cobalt, nickel).
❓ What is a Proton Exchange Membrane Fuel Cell (PEMFC)?
✅ A fuel cell that uses a polymer membrane as an electrolyte, allowing ion flow while preventing electrical conductivity.
❓ Where are PEMFCs used?
✅ Used in mobile and stationary applications (e.g., vehicles, backup power).
❓ How are PEM fuel cells categorized?
✅
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.
❓ What is a major weakness of LT PEM fuel cells?
✅ Carbon monoxide (CO) contamination, which can poison the membrane, requiring high-purity hydrogen.
❓ What is an Alkaline Fuel Cell (AFC)?
✅ A fuel cell that uses an alkaline electrolyte (e.g., sodium or potassium hydroxide).
❓ What is the typical operating temperature of an AFC?
✅ Below 100°C.
❓ What is the efficiency range of an AFC?
✅ 30-80% efficiency.
❓ What is a weakness of AFCs?
✅ Carbon dioxide (CO₂) reduces performance, affecting efficiency when exposed to air.
❓ What is a recent development in AFC technology?
✅ Anion Exchange Membrane Fuel Cells (AEMFCs), which use a solid anion-exchange membrane instead of liquid electrolytes, improving efficiency.
❓ What is electrolysis?
✅ Electrolysis is a process where electricity drives a non-spontaneous chemical reaction in an electrolytic cell.
❓ How is an electrolytic cell similar to a fuel cell?
✅ It works in reverse of a fuel cell, continuously using electricity to force a reaction.
❓ What is a common example of an electrolytic cell?
✅ A Downs cell, used to produce metallic sodium (Na) and chlorine (Cl₂) from sodium chloride (NaCl).
❓ Why is electricity required for electrolysis?
✅ The reaction has a negative standard potential, meaning it is non-spontaneous and needs an external energy source.
❓ What is the temperature at which a Downs cell operates?
✅ 801°C.
❓ How can hydrogen be produced using electrolysis?
✅ By using electricity to split water (H₂O) into hydrogen (H₂) and oxygen (O₂).
❓ How does this process relate to fuel cells?
✅ The electrolysis of water is the reverse reaction of a hydrogen fuel cell.
❓ What is electroplating?
✅ A process that uses electrolysis to deposit a metal coating onto a surface for protection or decoration.
❓ How does electroplating work?
✅ Electrons move from the anode to the cathode, causing metal ions (Mn⁺) to be reduced and form a solid metal layer on the cathode.
❓ What is an example of an electroplating reaction?
✅ The reduction of copper ions (Cu²⁺) to solid copper (Cu) at the cathode.
❓ What factors determine the exact half-reactions in electroplating?
✅ The electrolyte and the metal used for the coating.
❓ What is corrosion?
✅ The spontaneous oxidation of a metal surface, causing degradation over time.
❓ How does corrosion occur?
✅ The metal acts as an anode, where oxidation occurs, while oxygen is reduced to form water.
❓ How does corrosion relate to electroplating?
✅ Corrosion is the reverse of electroplating, where instead of depositing metal, the metal surface oxidizes and deteriorates.
❓ What constant is used to calculate the amount of metal deposited in electroplating?
✅ The Faraday constant (F).
❓ What formula determines the amount of metal deposited?
✅
(𝐼×𝑡)/(𝐹×𝑛)
where:
I = Current (Amperes)
t = Time (Seconds)
F = Faraday constant
n = Number of electrons needed for reduction
❓ How can you calculate the total weight of deposited metal?
✅ Multiply the moles of metal by its atomic weight.
❓ What are the units of the final deposited metal calculation?
✅ Grams (g).
