Electrochemical cells and electrode potentials Flashcards
What does a more positive E tell you?
it is a stronger oxidising agent
What does a more negative E tell you?
it is a stonger reducing agent
What is the standard electrode potential?
the emf (V) measured when a half cell is connected to a standard hydrogen half-cell under standard conditions
What is the role of the electrodes?
allows the flow of e-
What electrode is used for gases and when there is no solid metals present? and why?
platinum electrode Pt
it is inert = unreactive
How can you find the standard electrode potential of a reaction?
connect the half-cell containing the respective reaction to a standard hydrogen half cell
In what direction do electrons flow in terms of the value of E?
e- flows to the reaction with the more positive standard E
from the negative electrode to the positive electrode
What is the role of the salt bridge?
balances the charge of ions in the half-cells by allowing the controlled movement of ions between the two solutions
What is electroplating?
plating an electrode in solid metal
What need to be on a electochemical cell diagram?
the electrodes must be dipped in solution
salt bridge must be in solution and labelled
label the direction of e-
which electrode is recieving e- = positive and negative electrode labelled
standard conds
voltmeter reading
What are the standard conditions?
1 atm
298K
1 moldm-3
How is a salt bridge made?
a piece of filter paper soaked in potassium nitrate solution
What is a potential difference?
the difference in energy between two points in a circuit
At which electrode does reduction happen?
positive electrode
At which electrode does oxidation happen?
the negative electrode
At which electrode does oxidation happen?
the negative electrode
What is the standard cell potential?
the difference between standard E values
What does a more positive standard E value tell you?
the more likely that half equation will run forwards in the direction of reduction (e- gained)
What will happen if you increase the concentration of reactants on the left of the reaction? and what will this do to the standard E value?
the equilibrium will shift to the right - so reduction is more favoured and the standard electron potential will become more positive
What are the 2 limiting factors of standard electrode potential values?
not under standard conds
rates of reaction
How does a high activation energy affect the standard electrode potential?
high Ea may prevent a reaction from happening or making it very slow, therefore it may not reach equilibrium
standard E values are only a prediction of what could happen
What is a storage cell?
an electrochemical cell where the voltmeter is replaced by an electrically powered device
How can a cell be recharged?
possing a current through the cell in the opposite direction to the normal current = drives reactions in reverse and regenerated the reactants
What is a fuel cell?
an electrochemical cell which used the energy released by reaction of fuel with oxygen to generate a voltage
What is the cell potential of a hydrogen-oxygen fuel cell?
1.23 V
What is the overall reactio for a hydrogen-oxygen fuel cell?
H2 + 1/2 O2 –> H2O
Is the second electron affinity of oxygen exothermic or endothermic?
endothermic = requires energy to add a second electron to an already negatively charged oxygen ion O-
Which type of reaction has electrons on the left side?
reduction
