Electrochemical Cells Flashcards
What is the definition of electrochemical series
A list of electrode potentials in order
What will be the E° of the weakest and strongest reducing agent
Weakest - Most positive E°
Strongest - most negative E°
How do you calculate EMF of a cell
Most +ve - most -ve
How do you maintain the EMF of a fuel cell when in use
Keep the concentrations of reactants constant
State the substances and conditions needed in a standard hydrogen electrode
- H2 gas and 100kPa
- 1 mol dm^-3 and HCl
- Pt electrode and temperature of 298K
Explain how a salt bridge provides an electrical connection
Free moving Ions can move through it to maintain charge balance
Why is a high resistance voltmeter used
To stop the current from flowing in the circuit so you can measure the maximum possible potential difference
What will be the E° of the weakest and strongest oxidising agent
Weakest - Most negative E°
Strongest - most positive E°
On which sides of a half equation are the oxidising and reducing agents
Left - oxidising agents
Right - reducing agents
What’s the advantages of fuel cells
- greater efficiency
- less pollution and less CO2
What’s the drawbacks of fuel cells
- expensive
- limited lifetime
- hydrogen flammable so hard to store and transport
- toxic chemical in their production
What’s advantages to ethanol fuel cells compared to hydrogen
- can be made from renewable sources in a carbon neutral way
- less explosive and easier to store
Which half cell will be oxidised and reduced
More -ve half cell - is oxidised
More +ve half cell - is reduced
Why is a platinum electrode used
- it is unreactive
- it conducts electricity
It provides a surface for electron transfer
How does changing concentration of a reactant effect the EMF of a cell
Increased conc - increases EMF
Decreased conc - decreases EMF
Which half equation is always backwards when combining
Oxidation (the one with the more -ve emf)
How does the equilibrium shifting left effect EMF
EMF will decrease
What does electrode potential suggest about feasibility of a reaction
If EMF is +ve then reaction is feasible
If the electrode potential of something is greater than the other what does it mean for oxidation
If its EMF is greater then it CAN oxidise the other thing
If it’s EMF is not greater then it CANNOT oxidise the other
Why might the calculated EMF value differ from the commercial
Non standard conditions
What could be a reason why EMF decreases to 0
The concentration of ions becomes equal
What is the salt bridge made out of
KNO3 because all it’s salts are soluble so won’t form a precipitate with any ions in the half cells
Why might the emf of two of the SAME complex ions in a table be different
Different ligands
How would you write an equation for the reaction taking place in the cell while it is being recharged?
Combine the two half equations as normal and then reverse the whole equation
Why does a fuel cell not need to be recharged?
- there is a constant supply of the reactants/hydrogen fed in
How can you use half equations to explain how an electric current can be generated?
- name the thing getting oxidised and say that it produces electrons
- name thing getting reduced and say that it accepts electrons
