3.1 - Redox & SEP Flashcards
What is oxidation?
Oxidation is the loss of electrons
What is reduction?
Reduction is the gain of electrons
What is a redox reaction?
When both oxidation and reduction occur in the same equation simultaneously
What happens to the species in a redox reaction?
The species being oxidised loses the electrons which are then donated and gained by the other species which is being reduced
How do electrochemical cells use redox? (+ potential difference)
The electron transfer between products creates a flow of electrons, this flow of charged particles is an electrical current which flows between electrons in the cell.
Potential difference is produced between 2 electrodes which can be measured.
What are the rules for oxidation numbers?
- elements = 0
- neutral compounds = 0
- charged compounds = total of the charge
- hydrogen = +1 (ex. metalhydrides where its -1)
- oxygen = -2 (ex. peroxides and F2O where it is -1)
- all halogens = -1
- G1 metals = +1
What makes up an electrochemical cell?
2 solutions with metal electrodes, a voltmeter and a salt bridge
What does a salt bridge do in an electrochemical cell?
A salt bridge is a tube of unreactive ions that can move between the solutions to carry the flow of the charge but will not interfere with the reaction
Usually made out of KNO3 or KCl
Why are half equations used?
Used to show the separate oxidation and reduction reactions that occur in a redox reaction
How do you balance half equations?
- balance all species except oxygen and hydrogen
- balance oxygen using H2O
- balance hydrogen using H+ ions
- balance charges using e- (electrons)
How are standard cells represented?
- the half cell with the most negative potential goes on the left
- the most oxidised species from each half cell goes next to the salt bridge
- a salt bridge is shown using a double line
- always include state symbols
What is a cell potential?
If measured under standard conditions, cell potentials are measured compared to the standard hydrogen electrode (SHE) to give a numerical value for the half cell potential
What does a more positive cell potential mean?
The substances are more easily reduced and will gain electrons
What does a more negative cell potential mean?
The substances are more easily oxidised and will lose electrons
What is a standard hydrogen electrode and its conditions?
cell potential of 0.00V, measured under standard conditions
- solutions of 1 moldm-3 concentration
- temp of 298K
- 100kPa pressure
What does a standard hydrogen electrode consist of?
Hydrochloric acid, hydrogen gas and platinum electrodes
Why are platinum electrodes ideal for SHE?
Very useful as they are metallic,so they will conduct electricity but not interfere with the reaction
Whats the equation for cell emf?
emf (cell) = E* (right) - E* (left)
- most postive potential minus the most negative potential
- reduced species potential minus oxidised species potential
What does it mean if a cell emf if positive?
If the overall cell potential is a positive value, the reaction taking place is spontaneous and favorable
The more positive the cell potential, the more favourable the reaction
What is the anticlockwise rule?
- write the most negative emf out of the pair on top
- draw anticlockwise arrows around the reactions
- balance the electrons on both sides of the reaction
- write out the cell reaction
What are fuel cells?
Used to generate an electrical current wihout needing to be recharged
What is the most common type of fuel cell?
The most common type of fuel cell is hydrogen which uses a continuous supply of hydrogen and oxygen in the air to generate a continuous current
What is an advantage of using hydrogen fuel cells?
The reaction that takes place produces only water as a waste product, so relatively environmentally friendly
What is a disadvantage of using hydrogen fuel cells?
- energy is required to produce a supply of oxygen and hydrogen, for example electrolysis of water which requires electricity, indicating that hydrogen fuel cells are not carbon neutral
- hydrogen is highly flammable so requires careful storage
