Electrochemical Flashcards
All the electrochem stuff
Define Oxidation
loss of electrons at the anode and increase in oxidation number
Define Reduction
gain of electrons at cathode and decrease in oxidation number
What is a Direct reaction?
a spontaneous reaction that doesn’t require an external source of energy
What is an Indirect reaction?
2 different solutions are separate as have external energy source
Limitations of electrochemical series
- only have voltages at SLC
- doesn’t state the rate of reactions when 2
substances mix - concentrations have to 1M; doesn’t have any others
How do you do KOHES in a BASIC solution?
KOHES + 2 steps (1 is add OH- to both sides & 2 is cancel everything else out after H+ and OH- join to form water)
What is a primary cell?
- It cannot be recharged
- The amount of energy supplied is limited to the amount of reactants available within cell
What is a secondary cell?
- It can be recharged
- The reactants used to power devices can be reformed from the products of the discharge reactions
What are some factors impacting cell selection? (7)
- Initial & operating costs
- Size and shape
- Mass
- Memory affect
- Voltage
- Current
- Shelf life
What are fuel cells?**
A type of galvanic cell that has fuel consistently pumped in and electricity is continuously generated
*note: fuel is ALWAYS at anode & oxygen ALWAYS at cathode
What is an electrolyte?
- A solution that conducts electricity due to ions being able to flow past each other.
- May be a molten ionic compound or a dissolved ionic compound.
Why do fuel cells use porous electrodes?
- the electrodes are made from material with many holes (pores)
- this allows a GREATER surface area for reaction to take place thus a GREATER rate of reaction
- also allows reacting gases to access electrolyte.
What are some advantages of a fuel cell with hydrogen as the fuel?
- lower emissions of harmful sulfur/nitrogen containing compounds
- low maintenance and running costs
- QUIET
- No direct CO2 emissions
- Greater efficiency than direct combustion
What are some disadvantages of a fuel cell with hydrogen as the fuel?
- Storage and safety issues with highly explosive hydrogen fuel
- Expensive to manufacture (especially porous electrodes)
- Requires new infrastructure for hydrogen fuels (eg. fuel stations)
- Potentially still not as efficient or convenient as batteries
Compare Fuels cells and Combustion reactions
- Fuel cells have a higher energy efficiency whereas combustion reactions have a lower energy efficiency
- Fuel cells are (generally) more expensive whereas combustion reactions are cheaper
- Fuel Cells pollutants depend on fuel used whereas combustion reactions pollutants can include CO2, CO or NO2
- Fuel cell have one energy transformation (chemical-> electrical) whereas combustion reactions have many many energy transformations
- Fuels cells are quieter whereas combustion reactions are nosier
What are some disadvantages for using hydrogen fuel?
- Hydrogen is highly flammable and can be explosive = dangerous
- Hydrogen is odourless, tasteless and colourless = difficult to detect leaks
- Very difficult to safely store
- Flames of burning hydrogen are almost invisible = difficult for fire fighters
What is Faraday’s First law?
The quantity of electric charge (i.e Q in coulombs) carried by a given galvanic cell is directly proportional to the mass lost from the anode or gained at the cathode
*What is Faraday’s Second law?
- For a given starting amount of anode, the number of mols of electrons produced by a galvanic cell is directly proportional to the coefficient of electrons in the balanced oxidation half-equation
e.g: start 1 mol Ag atoms at anode
Ag-> Ag+ + e-
coefficient of e- is 1 thus 1 mol
What is Faraday’s constant?
96500 C
What is Avogadro’s constant?
6.02 x 1023 mol-1
In galvanic cells, what are the charges of the electrodes?
Anode = negative
Cathode = positive
In electrolysis, what are the charges of the electrodes?
Anode = positive
Cathode = negative
What is an electrolytic cell?
- A cell that uses an electric current (DC) to force a chemical reaction to occur that would otherwise not happen.
- Composed of two electrodes in an electrolyte that is commonly an aqueous solution or molten ionic compound.
What is special about using molten substance and not aqueous?
NO WATER IS INVOLVED
What is the energy shift in discharge and in recharge for a secondary cell?
- Discharge (galvanic) = chemical energy -> electrical energy
- Recharge (electrolysis) = electrical energy->
chemical energy
What conditions must be present in order for a secondary cell to be recharged?
- Products of discharge must stay in contact with electrodes
- Voltage is higher than the voltage produced when discharging in order to fully recharge
- positive terminal of power supply connected to positive terminal of cell and same for negative terminals
For discharge and recharge, what are the charges of the anode and cathode?
- Discharge = anode: negative & cathode: positive
- Recharge = anode: positive & cathode: negative
What are some common secondary cells?
- Lead-Acid battery
- Nickel-Metal Hydride
