Electrode Potentials Flashcards
When is dynamic equilibrium achieved
When the rate of ions leaving = rate they are joining
What are the conditions for a SHE
Platinum electrode
1 mol dm^-3 of hydrogen ions
H2 gas at 100kPa
Temperature of 298K (25°C)
How can you tell which goes on the left when comparing cells
Most negative goes on the left
Oxidation is on the left
What is the definition of emf
The potential difference measured when two half cells are connected
What is the definition of standard electrode potential
The potential difference measured when a half cell is connected to the standard hydrogen electrode under standard conditions
What does the standard electrode potential allow you to do
Compare position of equilibrium
More negative = left
More positive = right
How do you measure the emf of a cell
EMF = voltage on right - voltage on left
Biggest number - smallest number
How do you use the emf of a cell to predict if a reaction will occur
- Write full equation for reaction
- Split into two half equations
- Add together the emf of the the two half equations
- If Ecell is positive then the reaction is feasible
What direction do electrons flow
From negative electrode to positive
Where there are lots of electrons to little
What happens in a SHE
H2 flows over pours platinum
Equilibrium set up between H2 and H+ ions
Catalysed by platinum
What is the salt bridge in an SHE and what does it do
Glass tube filled with electrolyte
Ions complete the circuit and the ends are stoppered to stop mixing of salt bridge contents and beakers
What are 3 positives of Hydrogen fuel cells
Renewable
Silent
No pollution as the only product is water
What is a characteristic of primary cells
Single use and non rechargeable
What is the characteristic of secondary cells
Rechargeable so multiple use
What is the characteristic of fuel cells
They continually produce current if there is enough fuel
If there is an increase in E° values will the thing be a better reducing agent or oxidising agent
A better oxidising agent
Is the E° value is more negative will the agent be a better reducing or oxidising agent
Stronger reducing agent
How do you use E° to predict if a reaction will occur
- Write full equation
- Split into two half equations
- Add together the E° for the two half equations
- If Ecell is positive then the reaction is energetically feasible
What is are the oxidation and reduction reactions in a Zinc-carbon cell
See notes
What is the overall equation for a zinc-carbon cell (primary cell)
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What are the oxidation and reduction reactions of a lithium ion cell (secondary cell)
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What is the overall equation for the reaction of a lithium ion cell (secondary cell)
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What is the use of graphite in a lithium ion cell
Support medium
Water would react with lithium
How is a lithium ion cell recharged
Ions move from positive to negative so reactions are reversed
What is the conventional cell representation of a lithium ion cell
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What are the oxidation and reduction reactions for an alkaline hydrogen-oxygen fuel cell
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What is the overall equation for the reaction of an alkaline hydrogen-oxygen fuel cell
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What is the cell convention for an alkaline hydrogen-oxygen fuel cell
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