Electrode Potentials

These flashcards cover key concepts related to redox equilibria and electrochemical cells, as outlined in the provided lecture notes.

What are the two main components of an electrochemical cell?

Two half-cells connected by a salt bridge.

What does a salt bridge do in an electrochemical cell?

It connects the two half-cells and allows the flow of charge through free-moving ions.

What is the purpose of a high resistance voltmeter in measuring E?

To prevent current flow and allow measurement of maximum potential difference.

In cell diagrams, what does a double vertical line represent?

The salt bridge between two half-cells.

What must be included in a cell diagram if no solid metal electrode is present?

A platinum electrode.

What is the standard hydrogen electrode (SHE) assigned as?

A potential of 0 volts.

What are the necessary conditions for establishing a standard hydrogen electrode?

100 kPa hydrogen gas, 1 mol/dm³ H+ solution, 298K temperature, platinum electrode.

What is the significance of standard electrode potentials?

They are measured against the standard hydrogen electrode.

What happens to the equilibrium of a redox reaction if reactant concentration increases?

The equilibrium shifts to favor the products.

How do temperature changes affect the Ecell of a reaction?

Increasing temperature generally decreases Ecell for exothermic reactions.

What are examples of secondary standards in electrochemistry?

Silver/silver chloride and calomel electrodes.

How do we calculate Ecell using standard electrode potentials?

Ecell = Ered - Eox.

What does a positive Ecell indicate?

That the reaction will occur spontaneously.

What is a dry cell?

A non-rechargeable cell that generates electricity through chemical reactions.

What forms the electrolyte in a hydrogen fuel cell?

Typically, potassium hydroxide (KOH) solution.

What is the overall reaction in a hydrogen fuel cell?

2H2 + O2 → 2H2O.

What is the effect of using a platinum electrode?

It provides a conducting surface for electron transfer without participating in the reaction.

What should you do to improve electrical contact when constructing an electrochemical cell?

Clean electrodes with sandpaper and wipe with propanone.

What does the vertical line in a cell diagram indicate?

The phase boundary

What must be true about the concentration of solutions in standard conditions?

All solutions must be at 1 mol/dm³.

What does the term 'oxidizing agent' refer to?

A substance that gains electrons and is reduced.

What does the term 'reducing agent' refer to?

A substance that loses electrons and is oxidized.

What is the equation for the hydrogen half-reaction?

H2(g) → 2 H+(aq) + 2e-.

What happens to the potential of a half-cell when it is connected to a hydrogen electrode?

The potential difference can be measured relative to the SHE.

What is the significance of comparing E⦵ values?

To predict the direction of redox reactions.

What happens to the potential difference as reactants get consumed?

The Ecell approaches zero as the reaction proceeds.

Which electrode undergoes reduction?

The more positive electrode in the redox couple.

What is the overall goal of using standard electrode potentials?

To determine spontaneity and direction of redox reactions.

What conditions are typically required for a spontaneous redox reaction?

Positive cell potential (Ecell > 0).

What is a primary non-rechargeable cell example?

A dry cell or alkaline battery.

What is a lead-acid cell used for?

It is a type of rechargeable battery commonly used in cars.

What electrochemical process occurs during recharging of cells?

The direction of the electrochemical reactions is reversed.

What occurs with lithium-ion cells during discharging?

Lithium ions move from the anode to the cathode.

What are the disadvantages of hydrogen fuel cells?

• Difficult to store and transport

• Hydrogen is readily available via electrolysis but that is expensive

• HIgh production costs

• Limited lifetime

• Use of toxic chemicals in production

What are common uses for nickel-cadmium batteries?

Powering electrical equipment such as drills and shavers.

Why are aging fuel cells problematic?

Limited lifetime requiring regular replacement.

What happens in a fuel cell?

A fuel reacts with oxygen to create a voltage.

What do fuel cells provide over conventional engines such as petrol/diesel?

Higher efficiency and lower pollution and less CO2.

What is the half-reaction for ethanol in a fuel cell?

C2H5OH + 3H2O → 2CO2 + 12H+ + 12e-.

What are the advantages of ethanol fuel over hydrogen fuel?

• Doesn’t require new infastructure

• Made from renewable sources

• Less explosive

• Easier to store

• Abundant raw materials for the fermentation process

Which electrode reaction in a hydrogen fuel cell is oxidation?

2e- + 2H2O → H2 + 2OH-.

What is the effect of increased concentration on Ecell?

Increased reactant concentration typically increases Ecell.

What are typical conditions for obtaining standard electrode potentials?

1 mol/dm³, 298K, and 100 kPa, no current flowing.

What role does the platinum surface play in electrode reactions?

It acts as a catalyst and does not partake in the reaction directly.

What is Ecell?

A measure of how far from equilibrium the cell reaction lies.

What is a salt bridge made from?

Filter paper soaked in salt solution.

Why is ametal wire not used?

It would create its own electrode system, interfering with the results.

Where does the more positive half-cell go in a cell diagram?

On the right.

What is the platinum wire that is used coated in?

Platinum black that is porous and has a large surface area for absorption of hydrogen gas.

Why are standard conditions important?

The position of redox equilibrium changes with conditions.

Where do the most powerful reducing agents go on an electrochemical series?

Most negative end

Where do most powerful oxidising agents go on an electrochemical series?

Most positive end.

What are the conditions in a fuel cell?

Constant supply of H2 and O2 which maintains a constant voltage over time, so there is a constant concentration of reactants.