Redox Flashcards
What is reduction and oxidation
What is redox
Oxidation - loss of electrons
Reduction - Gain of electrons
A reaction which involves both oxidation and reduction
What are reducing agents
What are oxidising agents
Reducing agent - Species which lose electrons but themselves are oxidised
Oxidising agent - Species which gain electrons but themselves are reduced
What are the oxidation state rules
- Uncombined elements always have state 0 (Fe = 0)
- Oxidation number on ions is same as charge on ions (Ca2+ = +2)
- Group 1 have oxidation state of +1
- Group 2 have oxidation state of +2
- Aluminium has state of +3
- Hydrogen has +1, except in hydrides where it’s -1 (eg. NaH)
- Chlorine is -1 except when it’s in compound with F or O
- Fluorine is ALWAYS -1
- Oxygen is -2, except on peroxides where it’s -1/in OF2 where it’s +2
Standard electrode potential
potential difference of a half cell compared with a standard hydrogen half cell under standard conditions
Standard conditions: 298K, solutions of 1 mol dm-3 concentrations, 100 kPa
Give reasons why it is uncertain whether reactions predicted from E o values may
actually take place.
High activation energy
Conditions not standard
Disadvantages of hydrogen fuel cells
H2 is gas so difficult to transport
Hydrogen is flammable
Difficult to manufacture
State important differences between a fuel cell and a conventional electrochemical
cell
A fuel cell converts energy from reaction of a fuel
with oxygen into a voltage
Write the equation for the overall reaction that takes place in a hydrogen fuel cell
2H2 + O2 –> 2H2O
State ways that hydrogen might be stored as a fuel for cars
under pressure
adsorbed on solid
adsorbed on liquid
Suggest why some people consider that the use of hydrogen as a fuel for cars consumes
more energy than using fossil fuels such as petrol and diesel
Energy is needed to make the hydrogen
