11: Electrochemical Cells Flashcards
What type of reaction occurs at the electrode in a cell?
Reversible half equation
Describe how to set up an electrochemical cell.
Set up 2 beakers filled with a liquid and place 2 metal electrodes in. Join these electrodes with a voltmeter. Join the beakers with a salt bridge.
Describe the electrode potential that is likely of a metal that is easily oxidised.
Very negative
Describe the electrode potential that is likely of a metal that is easily reduced.
Less negative (or more positive)
What does R l O ll O l R stand for?
Reduced Oxidised Oxidised Reduced
One l shows one side of the equation for each of the half cells
ll represents a separation between the 2 half cells
How do we arrange ROOR equations?
The more negative half cell is always on the left.
When must we rearrange some half equations when setting up cells?
The more negative one must be rearranged and the less negative one stays as it is.
Why do some half cells require a platinum electrode?
When both ions in a half cell are aqueous.
How do we represent a half cell with a platinum electrode in a ROOR equation?
We add Pt l R l O I O I R l Pt (doesn’t have to be both electrodes, depends on which equations are aqueous)
Why do more reactive metals have a lower electrode potential?
Because they want to lose their electrons more.
Describe the how we set up a standard hydrogen electrode.
Bubble H2 gas through a solution of aqueous H+ ions and use a Pt electrode.
Give the standard conditions needed when measuring electrode potentials under the standard hydrogen electrode.
1 moldm-3, 298k, 100kPa
In ROOR equations, will the standard hydrogen electrode always be seen on the left or right, regardless of which electrode is more negative?
Left
Give an equation used when calculating the overall electrode potential of a cell.
Electrode potential of cell = E (RHS) - E (LHS)
For non metals, what does a more positive electrode suggest about reactivity?
More reactive
Why are metals good reducing agents?
Because they give away electrons.
How do we know if a reaction is feasible from a redox equation?
Write the 2 half equations and ensure the more negative one is flipped. Combine the equations.
If the reaction is feasible, the overall electrode potential will be positive.
Explain how the salt bridge provides an electrical connection between 2 solutions in a cell.
Allows for movement of ions.
When the voltmeter is replaced by a bulb, the EMF of the cell in Figure 2 decreases
over time to 0 V
Suggest how the concentration of copper(II) ions in the left-hand electrode changes
when the bulb is alight.
Give one reason why the EMF of the cell decreases to 0 V
Copper ions in left hand electrode increase.
EMF decreases to 0v because Cu2+ ion conc in both solutions
Describe what happens inside a non rechargeable cell.
An irreversible reaction occurs
Describe what happens inside a rechargeable cell.
A reversible reaction occurs
What are fuel cells?
Cells powered by an external source of fuel
Give the equation that occurs at the negative electrode in a hydrogen fuel cell.
2H2 -> 4H+ + 4e-
Give the equation that occurs at the positive electrode in a hydrogen fuel cell.
O2 + 4H+ + 4e- -> 2H2O
Give an advantage and disadvantage of non rechargeable cells.
+ Cheap
- Difficult to dispose of
Give an advantage and disadvantage of rechargeable batteries.
+ Reusable
- More expensive than non rechargeable
State what must be done to maintain the EMF when a fuel cell is in use.
Fuel must be constantly supplied.
