Redox equilibria Flashcards
1
Q
Describe a standard hydrogen electrode
A
- Hydrogen gas bubbled through
- 1.0 mol dm–3 HCl to make H+
- At 298K and 100kPa
- Pt electrode
2
Q
Why is the electrode potential 0 for H?
A
By definition
3
Q
Why do we use porous ceramic materials?
A
- Increases the surface area
- so faster rate of reaction
4
Q
Advantage of fuel cell over re-chargeable cell
A
- Can operate continuously without stopping to recharge
- Hydrogen and oxygen supplied continuously in fuel cell
5
Q
Why fuel cells aren’t really carbon neutral
A
- Hydrogen may need to be made using an energy source that is not ‘carbon neutral’
6
Q
Why does the cell emf change when a current flows
A
- The concentration of the ions change
- measurements no longer standard
- the e.m.f is determined when no current flows
7
Q
What is the purpose of a salt bridge and what is it made from?
A
- Allows ions to move between electrode, carrying charge
- Made from KNO3
8
Q
Features of Pt
A
- Conducts electricity
- Unreactive
- Does not create a potential difference
9
Q
Why does the voltage in a ‘lead-acid’ changes over time?
A
- Reagents are being used up so the concentration decreases
10
Q
What is the type of cell that has a constant voltage and why is it constant?
A
- Fuel cell
- Reagents are constantly supplied
- Concentration of reagents remain constant
11
Q
Features of salt bridge (KNO3)
A
- Inert, so it does not react with either electrode
- Allow electrical connection between electrodes
- The ions in the ionic substance in the salt bridge move through the salt bridge
12
Q
Features of porous separator?
A
Allows ions to pass through it
13
Q
Function of C(s) in the cell
A
Allows electrons to flow (conductor)
14
Q
Why does leaking occur with non-rechargeable cells?
A
- Metal (Zn) is ‘used up’
15
Q
Advantage of using rechargeable batteries over non-rec
A
- Does not leak
- No landfill problems as less waste
- less energy needed for mining
