5.2.3 Electrode Potentials Flashcards
what is standard electrode potential?
- the emf (voltage) of a half cell compared with the standard hydrogen half cell
- measured at 298K, solutions 1moldm-3, gases 100kPa
what is the half cell for a solid and and aqueous ions?
- metal solid in solution
what is the half cell for gas and aqueous ions?
- Pt metal
- hydrogen gas (see notes)
what is the half cell for 2 aqueous solutions?
- Pt metal
- both aqueous solutions
what else needs to be drawn in an electrochemical cell drawing?
- salt bridge
- voltmeter
why is platinum used?
- inert electrode
what is a salt bridge?
- filter paper soaked in an inert soluble substance e.g. potassium nitrate
- it allows ions to flow but not electrons
what is the electrode potential of hydrogen?
0V
which is the positive terminal?
- the cell with the more positive E0-
- the reaction will go forwards and gain electrons (reduction)
which is the negative terminal?
- the cells with the more negative E0-
- the reaction will go backwards and lose electrons (oxidation)
which way do electrons flow?
- negative to positive
how to work out Ecell?
more positive E0- - more negative E0-
how to predict the feasibility of a reaction?
- the equation with the more positive electrode potential will go forwards (gains electrons, reduction)
- the equation with the more negative electrode potential gas backwards (loses electrons, oxidation)
- state effect on position of equilibrium too
what are the limitations of predicting feasibility?
- non-standard conditions
- rate too slow due to high activation energy
- larger difference in electrode potentials = less likely to take place
when do non-rechargeable cells stop working?
- when the chemicals have reacted
how are rechargeable cells recharged?
- cell reaction can be reversed
- e.g. lithium cells
- disadvantages: toxicity, danger of fires, need recharging
how do fuel cells work?
- a fuel cell uses the energy from the reaction of a fuel with oxygen to create a voltage
- the reactants flow in and the products flow out while the electrolyte remains in the cell so they can operate continuously
what are the advantages of fuel cells?
- don’t have to be recharged
- work continuously as long as there is a supply of fuel and oxidant
Which way does the equilibrium shift?
- most negative system equilibrium shifts left
- most positive system equilibrium shifts right