Redox Flashcards
in a peroxide ?
O = -1
redox =
reduction reaction + oxidation reaction
oxidation number?
no. of electrons, lost gained or shared when an element reacts
half reactions overall give
ionic equation
oxidising agent?
are reduced, CAUSING OXIDATION
Reducing agent?
are oxidised, CAUSE REDUCTION
Can’t do half equations when
molecules involved bc no e- transfer
when reactions are in aq solution?
• H20, H+ present so use these to balance
to get overall eq?
- e- number must be same in each equation
* cancel anything that comes up on both sides
if O bonded to F?
no longer -2
if H is in a hydride?
no longer +1
No. of change in ox =
no of change in reduction
balance using Ox numbers?
- balance spectator ions last
* if 2 of the species (little no.) , x2 the number of change
A half cell
element in 2 diff oxidation states
electrode potential symbol
Eθ
Why is an inert electrode needed when there is an ECC w ions in diff ox states?
e.g. Pt or C bc no solids so can’t just dip crocodile clips into solution
how are SEP measured?
by connecting half cells to a SHE and measuring the PD
Half cells can be combined to form?
an electrochemical cell
salt bridge?
- connects the 2 solutions allowing ions to be trans between 2 half cell, completing the circuit
- doesn’t react w solutions in half cells
- KNO3 (aq) usually, has to have a conducting solution
the more + value is the
reduction
conc of solutions in half cells?
1moldm-3
SEP is
the tendency to gain e-
SEP definition?
voltage of a half cell compared to SHE measured at 298K, 100kPa, 1 moldm-3
eq to calc Eθcell?
Eθ positive -( Eθ negative)
or Eθ reduced - Eθ oxidised
Eθ NOT
measured by mole, don’t multiply up
when changing a conc look at
both equations!!
Positive Eθ =
feasible
⭐ can only change [] of
(aq) ions not solid
how to work out the best reducing agent?
- smallest E theta value
* least likely to be reduced
oxidising/ reducing agent?
• write the right species e.g. for reducing agent write the thing that is ABOUT TO BE oxidised
types of electrochemical cells?
- used as cells and batteries
- non-rechargeable cells
- rechargeable cells
- fuel cells
lead-acid battery: negative electrode?
Pb
lead-acid battery: positive electrode?
PbO2
lead-acid battery: electrolyte?
Sulfuric acid
one disadvantage of use lead acid battery in cars?
- Pb is heavy
- acid may leak out and corrode vehicle
- may be no charge left in battery - may go flt
what is a fuel cell?
an electrochemical device that combines hydrogen or a hydrogen rich fuel and O2 to produce electricity with water and heat as its by product
Fuel cells: fuel
- a log as fuel is supplied, fuel cell will continue to generate power - doesn’t need to be disposed of or recharged
- Since the conversion of fuel to energy takes place via an ECC process not combustion, the process is clean (no CO2 produced), quiet and high efficient
fuel cell overall equation
half equations for ox and red add together to give the same overall eq as combustion
what is reduced in a fuel cell?
oxygen, at cathode to water
what is oxidised in a fuel cell?
fuel , to CO2 at anode
the fuel always
gets converted into CO2, but not if fuel is H2
rechargeable and non-rechargable ECC are called
storage cells
+ of rechargeable cell?
can be used many times
+ of non- rechargeable cell?
cheaper
+ of fuel cell?
efficent, clean and quiet
fuels for fuel cell?
- alcohol
- alkanes
- alkenes
- hydrogen
problem w hydrogen fuel cell?
- H2 = explosive
* not universally available
