Electrochemistry

What is a dry cell?

A dry cell is a type of electrochemical cell that uses a paste electrolyte, making it portable and less prone to leakage.

What is a Leclanché cell?

A Leclanché cell is a type of primary cell that uses ammonium chloride as an electrolyte and is commonly used in batteries for small devices.

What are the main components of a Leclanché cell?

1. Zinc anode. 2. Carbon cathode. 3. Ammonium chloride paste electrolyte.

Describe the chemical reaction in a Leclanché cell.

The oxidation reaction at the anode involves zinc losing electrons, while the reduction at the cathode involves the ammonium ion.

What is the output voltage of a Leclanché cell?

The Leclanché cell typically provides an output voltage of about 1.5 volts.

What is a mercury cell?

A mercury cell is a type of primary cell that uses mercury oxide as a cathode and zinc as an anode, known for its stable voltage.

What is the main advantage of a mercury cell?

The mercury cell has a very stable voltage output and a long shelf life, making it suitable for precision devices.

What are the disadvantages of mercury cells?

1. Toxicity of mercury. 2. Environmental hazards for disposal.

What is a lead-acid battery?

A lead-acid battery is a type of secondary cell that stores electrical energy chemically, using lead dioxide and sponge lead as electrodes.

What is the nominal voltage of a lead-acid battery?

A fully charged lead-acid battery has a nominal voltage of about 2 volts per cell.

What are typical applications of lead-acid batteries?

Lead-acid batteries are commonly used in vehicles, UPS systems, and for starting engines.

Explain the overall reaction in a lead-acid battery during discharge.

$PbO_2 + Pb + 2H_2SO_4 \rightarrow 2PbSO_4 + 2H_2O$.

What is a nickel-cadmium (NiCd) cell?

A nickel-cadmium cell is a type of rechargeable battery that uses nickel oxide hydroxide and metallic cadmium as electrodes.

What is the advantage of NiCd cells?

NiCd cells have a long cycle life and can withstand deep discharges with resilience to repeated charging cycles.

What are the disadvantages of NiCd cells?

1. Memory effect. 2. Toxicity of cadmium. 3. Lower energy density compared to other rechargeable cells.

What is a hydrogen-oxygen fuel cell?

A hydrogen-oxygen fuel cell generates electricity through the electrochemical reaction of hydrogen and oxygen, producing water as a byproduct.

Describe the overall reaction in a hydrogen-oxygen fuel cell.

$2H_2 + O_2 \rightarrow 2H_2O + \text{Energy}$.

What are the main applications of fuel cells?

Fuel cells are used in transportation (e.g., hydrogen fuel cell vehicles), stationary power generation, and backup power systems.

What is the difference between primary and secondary cells?

Primary cells are disposable and cannot be recharged (e.g., dry cells), while secondary cells can be recharged (e.g., lead-acid batteries).

Explain cell notation.

Cell notation represents electrochemical cells, showing the anode, electrolyte, and cathode in the form: Anode | Electrolyte || Electrolyte | Cathode.

What are anodes and cathodes?

Anode is the electrode where oxidation occurs; cathode is where reduction takes place in an electrochemical cell.

What is the role of the electrolyte in a cell?

The electrolyte conducts ions between the anode and cathode to complete the electrical circuit.

Define half-cell reaction.

A half-cell reaction is either the oxidation or reduction process occurring at an electrode during electrochemical reactions.

What is cell potential?

Cell potential is the voltage difference between two electrodes, indicating the driving force of the electrochemical reaction.

What factors affect cell potential?

1. Concentration of reactants/products. 2. Temperature. 3. Nature of the electrodes and electrolyte.

How does temperature affect the cell potential according to the Nernst equation?

Increasing temperature generally increases the reaction rates, affecting cell potential through the Nernst equation: $E = E^\circ - \frac{RT}{nF} \ln Q$.

What is the advantage of using fuel cells?

Fuel cells provide high efficiency and low emissions, producing only water as a byproduct when using hydrogen as a fuel.

What are the disadvantages of fuel cells?

1. High cost of materials. 2. Hydrogen storage difficulties. 3. Limited infrastructure for refueling.

Describe the common misconceptions about batteries.

1. All batteries can be recharged. 2. Batteries are interchangeable without consideration for type and specifications.

What is a one-line revision fact for dry cells?

Dry cells are portable batteries using a paste electrolyte, widely used in household devices.

What is a one-line revision fact for lead-acid batteries?

Lead-acid batteries are rechargeable batteries with a nominal voltage of 2 volts per cell, commonly used in vehicles.

Recapitulate the working principle of nickel-cadmium cells.

NiCd cells work by reversible reactions involving nickel oxide hydroxide and cadmium, providing a reliable power source.

Identify one misconception associated with NiCd cells.

The memory effect in NiCd cells does not mean they can only work well when fully discharged before recharging.

Summarize the overall reaction for a mercury cell.

$Zn + HgO \rightarrow ZnO + Hg + \text{Electricity}$, providing stable energy output.

State NCERT's definition of an electrochemical cell.

An electrochemical cell is a device that converts chemical energy into electrical energy or vice versa through redox reactions.

What is a common use for mercury cells?

Mercury cells are often used in watches, hearing aids, and small electronic devices due to their compact size and stable voltage.

Explain the efficiency of lead-acid batteries.

Lead-acid batteries typically have an efficiency ranging from 70% to 90%, depending on charging and discharging conditions.

What role does an electrolyte play in a fuel cell?

In a fuel cell, the electrolyte allows the migration of ions while preventing the direct mixing of fuel and oxidizer, maintaining the electrochemical reaction.

Summarize the applications of hydrogen fuel cells.

Hydrogen fuel cells are used in transportation (fuel cell vehicles), stationary power plants, and backup power systems for various applications.