Redox & electrode potentials
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What is the method to write a full harder half equation for transition metal reduction?
• Work out the change in oxidation number. If the metal’s oxidation number has fallen, it has gained electrons. If it has risen, it has lost electrons. • Add the electrons to the equation. • As all reactions take place in acidic conditions, add a H+. • Balance out the overall negitive charge with H+ ions. • Divide the amount of H+ ions by 2 to work out the number of waters, to balance the added hydrogens.
What is the definition of standard electron potential?
The emf of a half cell compared to a standard hydrogen electrode, under standard conditions
What is the equation to calculate E cell?
Most positive value - least positive value
What voltage does a hydrogen fuel cell have?
0.00 volts
What things need to be included on an electrochemical cell diagram?
• Voltmeter • Wiring • Salt bridge • Electrodes & solutions. • If both equations don’t involve a solid either being made or lost, an inert platinum electrode must be used. • If 1 (or both) reactants or products are solid, then the electrode should correspond with said reactant or product.
In an electrochemical cell, what are the standard conditions?
• 298K • 100 kPa • 1 mol dm-3 solutions
What is the method to combine 2 half equations?
• Keep the most positive equation the same but change the reversible sign to a -> • Flip the negitive equation around • Cancel the electrons and then combine the 2 equations to make an overall half equation
How do we know if a given reaction is possible from the E cell value?
If the overall cell voltage is positive, the reaction is possible
What are the limitations of using the E cell value to determine reaction feasibility?
• The value of E Cell gives us no indication on the rate of reaction • It only tells us the feasibility under standard conditions