Electrode potentials Flashcards
How is an electrochemical cell created
By joining 2 different half cells together
With electrochemical cells, what is needed to join the 2 half cells together
A wire
In electrochemical cells what does the voltmeter measure
The potential difference between the 2 half cells
Do electrons flow from a more reactive metal to a less reactive metal, or from a less reactive metal to a more reactive metal
From a more reactive metal to a less reactive metal
What is observed when the half cell loses the electrons
The electrode becomes thinner
What time of reaction is it when the half cell loses electrons and the electrode becomes thinner
Oxidation
What type of reaction occurs when the half cell accepts electrons and the electrode gets thicker
Reduction
What is the usual compound that creates a salt bridge
Potassium nitrate
What is the electrode potential measured in
Volts
What does the electrode potential tell us
How easily the half cell gives up electrons
When writing electrochemical cell equations, in what form at the equations written
In reduced form, so electrons are always on the left hand side
When given the electrode potential values, what does the more negative value indicate( oxidation or reduction)
Oxidation
When given the electrode potential values, what does the most positive value indicate (oxidation or reduction)
Reduction
What does SHE stand for
Standard hydrogen electrode
What is the electrode potential of SHE
O volts
When setting up a SHE, what are the conditions underwhich hydrogen enters the the system
- 298 K
- 100 kPa
What are the conditions when comparing electrode potential values
- Temp: 298 K
- Pressure: 100 kPa
- Concentrations of ions at 1 moldm^-3
What does the SHE allow us to find
The standard electrode potential of other half cells
When given a table of standard electrode values, what is the most powerful oxidising agent
The most positive standard electrode value
When given 2 equations and the electrode potential, which reaction would go forward
The equation with the more positive electrode potential
What does the electrode potential say
How much energy is released
When drawing electrochemical cells what are the features that you must include
- 2 half cells
- Wire
- Voltmeter
- Salt bridge
- 2 Electrodes
- The electrodes must be under the water
If the half cell is a metal, what is the electrode made of
The same metal
e.g. Fe2+ +2e- -> Fe
use a Fe electrode
If neither half cells include a metal, what electrode should you use
- An inert metal like platinum
- Or graphite
What is the role of a salt bridge
Balances charges
Does the salt bridge carry ions or electrons
Ions
How do you assign the positive or negative charge to the electrode
The electrode that receives the electrons is the positive electrode
When drawing an electrochemical cell, what should you draw on the wire and on the salt bridge
The direction the electrons/ ions flow
What is the electrode that is used when using a hydrogen half cell
Platinum
How do you use a hydrogen half cell
Use a platinum electrode and bubbles hydrogen gas over it using a glass tube
What is the standard electrode potential of a half cell
The voltage measured in a cell in which that half cell is connected to a standard hydrogen electrode, under standard conditions
What 2 gases are in fuel cells
- Hydrogen
- Oxygen
In a hydrogen fuel cell, what is oxidised the hydrogen or the oxygen
Hydrogen
In acidic conditions, what is the equation of a hydrogen fuel cell
Oxygen + 2Hydrogen -> 2 Water
In alkali conditions, what is the equation of a hydrogen fuel cell
Oxygen + 2 Hydrogen -> 2 Water
What are the main issues around hydrogen fuel cells
- Explosive
- Compressed into a small battery
- Producing the hydrogen may produce carbon dioxide, so no better than other batteries
