Unit 5 Redox Equilibria Flashcards
E°cell = ?
E°R - E°L
On which side does reduction occur?
Reduction on the right
What are the advantages of hydrogen fuel cells?
Clean, no greenhouse gases, produce a constant voltage provided fuel supply, hydrogen is ‘abundant’
What are the conditions under which a standard electrode potential is measured?
298K, 100kPa, and the solution of ions must have a concentration of 1.00 mol dm^-3.
Give one economic advantage, and one environmental disadvantage to the use of non-rechargeable batteries.
They are cheap to make.
They cannot be reused, and throwing them away wastes the energy and resources needed to manufacture them.
Give one safety risk caused by the use of hydrogen-oxygen fuel cells.
Hydrogen is highly flammable.
What three things make up the standard hydrogen electrode?
H2 gas being bubbled over a platinum electrode and an acid (such as H2SO4)
How can you tell if a reaction is feasible from redox potentials (electrode potentials)?
More negative reaction goes to left, more positive to right. If reactants are on wrong side of “–>” then reaction isn’t feasible under standard conditions
What does the circle mean in “E°cell”
Under standard conditions
Why use a high resistance voltmeter?
To stop the current from flowing in the circuit
The reactions won’t be happening as a result
What does the symbol E stand for?
The potential difference
What is the salt bridge usually made from?
A piece of filter paper soaked in salt solution
Why would using potassium chloride as the salt forming the salt bridge not be suitable for copper systems?
The chlorine would react with the copper to form complexes
In cell diagrams, what does a solid vertical line represent?
The boundary between phases
What does the double line represent in a cell diagram?
The salt bridge between two half cells
What must be used if a system doesn’t include a metal that can act as an electrode?
A platinum electrode
Why is a platinum electrode suitable?
It provides a conducting surface for electron transfer
Is unreactive
Can conduct electricity
How is the potential of all electrodes measured?
By comparing their potential to that of the SHE
What is the secondary standard?
A standard electrode that has been calibrated against the primary standard e.g silver chloride
Where will the most powerful reducing agents be found?
At the most negative end of the series on the right (lower oxidation number)
Where will the most powerful oxidising agents be found?
At the most positive end of the series on the left (higher oxidation number)
Why will fuel cells maintain a constant voltage over time?
Because they are continuously supplied with hydrogen and oxygen so maintaining the concentration of reactants
Limitations of hydrogen fuel cells
Expensive
Storing and transporting hydrogen is difficult
Limited lifetime and high production costs
Use of toxic chemicals in their production
3 ways in which hydrogen can be stored in fuel cells
As a liquid under pressure
Adsorbed on the surface of a solid material
Absorbed within a solid material
On which side of the cell representation is the SHE?
Always on the left hand side
Why can ethanol be considered to be a carbon-neutral fuel?
CO2 is released by combustion which is then taken up in photosynthesis
