Redox Equilibria Flashcards
What is a loss of electrons called?
Oxidation.
What is a gain of electrons called?
Reduction.
How do we balance half equations?
Using H^(+) ions and water.
What convention do we use when we draw electrochemical cells?
We put the cathode on the left, the anode on the right, with two parallel lines between them to represent a salt bridge. We put a single line between any phase changes.
How do we usually write half equations for electrode reactions?
As reduction reactions.
How do we calculate the emf of a cell?
Take the left hand side electrode potential from the right hand side electrode potential.
What is commonly used as an electrode, and why?
Platinum or graphite, because they are inert.
When can we use an electrode of the same metal as the ions in the solution?
When they are being oxidised/reduced from/to the solid state.
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 must the concentration of a solution be when measuring the standard electrode potential of a half cell?
1.00 mol dm^(-3)
On which side must the standard hydrogen electrode always be placed?
The left.
What electrode is used in a standard hydrogen electrode?
Platinum.
Why are the conditions important when measuring standard electrode potentials?
As the reactions at each electrode are reversible, the equilibrium position can ba affected by temperature, pressure and concentration. Any change in equilibrium position will change the cell potential. To be able to compare cell potentials, we must always measure them under standard conditions.
How are standard electrode potentials usually listed?
As an electrochemical series.
Do good oxidising agents have more negative, or more positive electrode potentials?
More positive.
Do good reducing agents have more negative, or more positive electrode potentials?
More negative.
How can we use electrode potential values to work out the direction of electron flow between half cells?
Electrons will always flow from the more negative electrode to the more positive.
What is the equation for calculating emf?
E(rhs) - E(lhs)
How can we use standard electrode potential values to predict the direction of a redox reaction?
The more negative one will be oxidised, and the more positive one will be reduced.
What is the electrochemical series?
An ordered list of equations using standard electrode potential values.
How do we know, when using standard electrode potential values, if a reaction is spontaneous?
It will have a positive value.
Give three types of cells.
Non-rechargeable cells, rechargeable cells, and fuel cells.
Which is negative, the anode or the cathode?
The cathode.
Does oxidation or reduction happen at the cathode?
Oxidation.
How can we use E0 values to predict the direction of a redox reaction?
The more negative value has to be oxidised, and the more positive value has to be reduced.
What is the difference between the chemical reactions occurring in a rechargeable battery and a non-rechargeable battery?
In a rechargeable battery the reactions are reversible, and in a non-rechargeable battery they are not.
Give some advantages and disadvantages of a non-rechargeable battery.
Advantage: good for gadgets that are only used for short period of time, have to be disposed of, work for longer in one go, less likely to contain toxic metals
Disadvantage: often release substances, more expensive in the long run, aren’t suitable for devices that need a lot of power, use more resources
Give some advantages and disadvantages of a fuel cell.
Advantage: doesn’t need recharging, no toxic chemicals, only waste product is water
Disadvantage: need energy to provide hydrogen and oxygen, process is not carbon neutral, hydrogen is highly flammable
What reaction happens at the cathode of a hydrogen-oxygen fuel cell?
2H2 –> 4H+ + 4e-
What reaction happens at the anode of a hydrogen-oxygen fuel cell?
O2 + 4H+ + 4e- –> 2H2O
