Flashcards in Chapter 3 - Converting chemical energy to electrical Deck (28):
When using oxidation numbers oxidation is an
increase in number
When using oxidation numbers reduction is a
decrease in number
what are the main oxidation number rules?
1. oxygen is always 2-
2.hydrogen in mostly 1+
3.in elemental form O.N is 0
4. O.N on a simple ion is its charge
5. in a covalent compound without O or H the more electronegative element has the lower O.N
Constructing half equations what do we do?
We look for conjugate pairs. If a reactant or product has more than just one element we need to take another molecule from the overall reaction and add it in too.
How to tell if it is an acidic or alkaline environment?
We first read the question carefully. We also look at the electrolyte.
H+ = acidic
OH- = alkaline
How do we balance in an alkaline environment>
We use KOHES but then just add OH- at the end to cancel out the H+. We add it to both sides and must cancel out the waters created.
What is a galvanic cell?
A cell that concerts chemical energy into electrical energy.
Why do substances in galvanic cells need to be separated?
As a galvanic cell uses spontaneous reactions. if the reactants were placed in the same container they would just react in the container and therefore the energy could not be harnessed and turned into electrical energy.
how to we calculate Standard electrode potential?
E˚cell = E˚cathode - E˚anode
What is standard electrode potential?
A galvanic cell's ability to produce a current. the values are based on how well a substance attracts electrons when compared to a hydrogen half cell.
more likely to attract electrons
less likely to attract electrons
Define a battery
A battery is a series of many cells connected to each other producing a large current
Define a cell
A cell is a single unit producing a current
What is a wet cell
A cell with a liquid electrolyte
What is a dry cell
A cell with a paste electrolyte
What is a primary cell
What is a secondary cell
Factors affecting selection of cells
-temperature of surroundings
- shelf life
-ease of disposal
What reactant is always at the cathode of a fuel cell
What does the electrolyte do in a fuel cell?
-Controls ion movement
-acts as a salt bridge/ maintains charge
Describe the electrodes of a fuel cell
-porous (allow molecules to pass into electrolyte)
-coated with catalyst
-allow for redox reactions to occur
-break up molecules (e.g: into electrons & protons)
Advantages of a fuel cell
-Have the potential to produce electricity forever as long as they are continuously supplied with fuel/reactants.
- less pollution released
Disadvantages of a fuel cell
-parts are expensive (electrodes coated with a catalyst)
-expensive to store fuels (like hydrogen gas)
What is "poisoning the catalyst"?
The less pure a substance is, the more likely it will poison the catalyst and render it useless. reaction would still occur but very slowly.
when asked to the polarities (e.g top and bottom) of a physical battery we think....
which substance is acting as the anode and cathode? then which ever is closer to the top has the same polarity. e.g: if zinc acts as the anode and zinc powder is closest to the top of a primary button cell, then the top is negative too
sometimes fuel cells are more efficient at very high temps and pressures. so why don't we use these conditions?
too expensive to maintain these conditions. satisfactory results can be achieved with less extreme conditions.