DM - Electrode potentials Flashcards
What are electrode potentials measured against?
Standard hydrogen electrodes.
What is the standard electrode potential of a half-cell?
The voltage measured under standard conditions when the half-cell is connected to a standard hydrogen electrode.
What are standard conditions?
1) Any solutions must have a concentration of 1.00 mol dm^-3.
2) Temperature must be 298K (25 degrees).
3) Pressure must be 100kPa.
Which side is the hydrogen electrode always shown on?
The left.
What is the value of the standard hydrogen electrode half-cell?
0.00V
What does the reading of 0.00V on the standard hydrogen electrode half-cell mean?
The voltage reading (whether it is positive or negative) will be equal to the standard electrode potential of the other half-cell (as the standard hydrogen electrode is 0.00V)
Whether the voltage reading is positive or negative depends on what?
Depends on which way the electrons flow.
What can you use standard electrode potentials to do?
Calculate the cell potential of an electrochemical cell.
Will the cell potential always be a positive or negative voltage?
Positive voltage
Why will the cell potential always be a positive voltage?
Because the more negative standard electrode potential value is being subtracted from the more positive standard electrode potential value.
What sort of standard electrode potential do reactive metals have?
Large negative electrode potentials.
Why do more reactive metals have more negative standard electrode potentials?
Because the more reactive a metal is, the more it wants to lose electrons to form a positive ion.
What sort of standard electrode potential do reactive non-metals have?
More positive electrode potentials.
Why do more reactive non-metals have more positive standard electrode potentials?
The more reactive a non-metal is, the more it wants to gain electrons to form a negative ion.
What is an electrochemical series?
A list of redox equilibria.
What does the electrochemical series show?
What is reactive and what isn’t.
How is the electrochemical series arranged?
In order of electrode potential. The redox equations with the most negative standard electrode potentials are at the top, and those with the most positive electrode potentials are at the bottom.
What does a more positive electrode potential mean?
1) The left-hand substances are more easily reduced.
2) The right-hand substances are more stable.
What does a more negative electrode potential mean?
1) The right-hand substances are more easily oxidised.
2) The left-hand substances are more stable.
What can you use electrode potentials to predict?
Whether a reaction will happen
How do you figure out if a metal will react with the aqueous ions of another metal using electrode potential values? (method)
1) Write the two half equations down as reduction reactions.
2) Look at the standard electrode potentials.
- The half-equation with the more negative electrode potential will move to the left.
- The half-equation with the more positive electrode potential will move to the right.
3) Combine the two half equations.
- If the direction of this redox reaction matches the reaction described in the question, it is feasible.
- If the correct ions are reacting together it is also feasible.
What does a prediction using standard electrodes only state?
Only states if a reaction is possible under standard conditions.
When could the prediction using standard electrode potentials be wrong?
If the reaction kinetics are not favourable.
If the conditions are not standard.
Why could the prediction using standard electrode potentials be wrong if the reaction kinetics are not favourable?
- The rate of reaction may be so slow that the reaction might not appear to happen.
- If a reaction has a high activation energy, this may stop it happening.
Why could the prediction using standard electrode potentials be wrong if the conditions are not standard?
Changing the concentration (or temperature) of the solution can cause the electrode potential to change.
- The shifting of the equilibrium may either reduce the ease of electron loss so an electrode becomes less negative and the whole cell potential decrease, or, it may increase the ease of electron gain so an electrode becomes more positive and the whole cell potential will be higher.
