Redox Equlibria Flashcards
What is oxidation and what is reduction
Oxidation is loss of electrons
Reduction is gain of electrons
What is an oxidising agent
A species that accept electrons while reducing another species
Electron pair acceptor
What is a reducing agent
A species that donates electrons to another species and they themselves are oxidised
Electron pair doner
What is meant by half cell
Is metal with metal ions in a solution
How does emf occur
As two different electrodes are connected,the potential difference between the two electrodes will cause a current to follow
What is the role of the salt bridge and what is it made from
It allows for ions to follow from one solution to the next to maintain the charge/complete the circuit
It’s a piece of filter paper that is saturated with a solution of KNO3 and NH4NO3
What is an electrochemical cell
The combination of two electrodes together
State what each electrode undergoes when current flows
The positive electrode is the one that favours the most reduction ie
The negative electrode will always favour oxidation
Why is the emf of the hydrogen electrode 0
By definition
In an electrochemical series what element will be the most powerful reducing agent
The one with the most negative value
In an electrochemical series which element will be the best oxidising agent
The one with the most positive value
What are the conditions for the standard hydrogen electrode and what is it used
Temperature at 298k
Pressure of 1atm
The species involved have a concentration of 1.0 mol dm-3
Platinum electrode
It’s used to measure the electrode potential of a half cell
State the direction of reaction fits its positive or negative
More negative it’s goes to the left
More positive goes to the right
How do you work out emf
EHRs-Elhs
State the difference between rechargeable and non rechargeable batteries
The current in rechargeable batteries can be reversed
What is meant by standard electrode potential
The emf of a half cell measured relative to the standard hydrogen electrode
State the direction the negative and positive half cell go
Negative will go backwards (oxidise
Positive will go forwards reduce
State the effect of concentration on E cell
If concentration of the reactants is increased e cell will increase
Same if concentration of products decreases
State the effect of temperature on e cell (fowatd reaction is exothermic)
If the temp increase their will be a decrease in e cell
If temp decrease increase due to le Chatiler
What is Ecell and what determines if the reaction happens
How far from equilibrium the cell reaction is how positive it is
When are cells non rechargeable
When the reactions/currents are non-reversible
Give the use of lithium ion cells
To power camera
Mobile phones
Why isn’t water used as a solvent in the lithium ion cell
As it will react with the lithium metal
What is the support medium in the lithium ion and what does it allow
It enables the ion to react with each other
Powdered graphite is the support medium
Give the equations for the lithium ion cell
Li+ +CoO2+e- ->Li+[CoO2]-
Positive
Li+ +e-> Li negative electrode
Li +CoCO2->LiCoCO2
What is a fuel cell give the overall reaction in a hydrogen fuel cell
It will use energy from the reaction of a fuel with oxygen in order to create a voltage they don’t need to be recharged
2H2+O2-> 2H20=1.23
Why aren’t standard conditions used in a fuel cell
The rate is too slow to produce an appreciable current
Give advantages of a hydrogen fuel cell
Less pollution and co2
Greater effecincy
Give limitation of a hydrogen fuel cell
Expensive
Use of toxic chemicals
Limited life time
Storing of hydrogen
State ways hydrogen can be stored in fuel cells
As a liquid under pressure
Adsorbed on the surface of a solid material or within a solid material
State why fuel cells maintain a constant voltage
They are continuously fed with fresh o2 and H2
What is the platinum electrode used for
To allow transfer of electrons
