Electrochemistry Flashcards
What is the purpose of the salt bridge?
To connect the two cells and to allow the ions to flow back towards the negative electrode
Which electrode is the positive electrode?
The cathode where reduction occurs.
Which electrode is the negative electrode?
The anode where oxidation occurs.
How to set up a cell diagram?
The lowest charges go on the outside
Why does the voltmeter have high resistance?
It has a very high resistance to stop a current flowing through the circuit to maximise the EMF produced.
What does a single line mean in a cell diagram?
Phase boundary
What does a double line in a cell diagram mean?
Salt bridge
What must you remember when drawing a cell diagram?
All the state symbols
Why is platinum used in an electrochemical cell?
It is very unreactive and can conduct electricity.
How do you separate species which are in the same phase in a cell diagram?
Use a comma
What is meant by the term ‘electrochemical series’?
List of electrode potentials in numerical order
What are the conditions for the hydrogen half cell potential to be 0?
100kpa 1mol 298K
Why would the actual EMF of a cell be different to the calculated one?
Not under standard conditions
Why should a hydrogen fuel cell be used instead of an internal combustion engine?
More of the potential energy is released from a fuel cell rather than an internal combustion engine.
Why should a hydrogen fuel cell be used instead of an internal combustion engine?
More of the potential energy is released from a fuel cell rather than an internal combustion engine.
Why would an electrode be rubbed with sandpaper prior to use?
To remove the oxide layer
What is a reducing agent?
An electron donor.
What is an oxidising agent?
An electron acceptor
Why cant some cells be recharged?
The reaction is not reversible
If it asks for the discharge equation what equation is it?
Just the normal oxidation then reduction
If it asks for a charging reaction what is the final equation
The one that normally gets oxidised is reduced and the one that normally gets reduced is oxidised
Why is the standard electrode potential for a hydrogen electrode 0?
By definiton
What salt solution should the salt bridge be dipped in and why?
Potassium nitrate and it should not react with either the electrodes or electrode solutions
If the system does not have a solid conducting surface, why should a platinum electrode be used?
unreactive and can conduct electricity
What is the standard electrode potential for strong reducing agents?
Most negative as they are being oxidised so losing electrons
What is the standard electrode potential for strong oxidising agents?
Most positive as they are being reduced so gaining electrons
What happens if you increase the concentration of the reactants?
The Ecell value will increase
What happens if you decrease the concentration of the reactants?
The Ecell value will decrease
How will temperature effect the value of Ecell?
If the temperature is increased then the value of Ecell will decrease the value of Ecell.
What is a fuel cell?
A fuel cell is a cell which uses energy from the reaction of a fuel with oxygen to create a voltage.
Why does a fuel cell maintain a constant voltage over a period of time?
The concentrations of the reactants and the products doesn’t change as they are constantly being replenished.
Why are high temperatures and high pressures used in fuel cells?
High temperature is needed because at standard conditions the Ecell value is too small, even though the forward reaction is exothermic. Therefore a high pressure is used as there are less moles of gaseous species on the right hand side so equilibrium shifts to the right.
What are the advantages of hydrogen fuel cells?
Less pollution from CO2
Hydrogen is readily available
good efficiency
What are the disadvantages of fuel cells?
expensive
storing and transporting hydrogen could be dangerous
toxic chemicals are used in their production
What components are needed for a standard hydrogen cell?
1 molar HCl
hydrogen
100kPa
platinum electrode
Why will the EMF of a cell reach zero?
The concentrations of the reactants and products are equal or the reactants have been used up.
How could recharging a cell lead to increased CO2 in the atmosphere?
power plant energy could come from burning fossil fuels
