Galvanic cells Flashcards
what is a galvanic cell
a type of electr-chemical cell in which chemical energy is converted into electrical energy
what is a salt bridge aka
the internal circuit
what does a salt bridge contain
filter paper soaked in a relatively unreactive electrolyte
electrolyte
chemical substance that conducts electric cureent
why are there two half cells in a galvanic cell
if the reactants come in contact with one another, their chemical energy is transformed directly into thermal energy, an external circuit transforms this chemical energy into electrical energy
what do half cells contaib
species that form a conjugate redox pair (an oxidising agent and its corresponding reduced form)
what are the three types of half cells
Half-cell containing metal conjugate pair, half-cell containing no metal conjugate pair and gas half-cell
half-cell containing metal conjugate pair
if one member of the conjugate pair is a metal it is used as the electrode, which is immersed in an aqeous solution containing the ions of the other conjugate pair
half-cell containing no metal conjugate pair
an inert electrode (platinum or graphite) is used as the electrode, immersed in a silver solution containing both of the conjugate pair
half cell containg gas
if one of the conjugate pair is a gas, these half cells usually contain other species not involved in the reaction, such as spectator ions and the solvent. Contains a platnum wire attached to a platinum electrode in a glass bell containg the gas
trend in strength of oxidant in electrochemical series
decreases in strength down the table
trend in strength of reductant in electrochemical series
increases in strength down the table
current
flow in a galvanic cell because one half-cell has a greater tendency to push electr;ns into the external circuit
potential difference
has the unit volt and is measured using a voltmeter
standard conditions of potential difference
a pressure of 100Kpa, 1.0M concentration of solutions, measured at 25 degress celcius
potential difference under standard conditions symbol
E°
how to calculate potential difference
E° of half cell conatining oxidant (higher cell) - E° of half cell containing reductant (lower cell)
is the voltage of the galvanic cell constant
no, they discharge and the cell voltage eventually drops to 0 and the cell is referred to as flat. equillibrium is reached
for it to be a spontaneous reaction, the E° must be
positive
for it to be a non- spontaneous reaction, the E° must be
negative
redox reactions
involve the transfer of electrons from one chemical species to another
oxidation numbers
a number assigned to an element to determine if a chemical reaction is classified as a redox reaction
increased oxidation number of an element means
the element has been oxidised and is the reductant
decreased oxidation number of an element means
the element has been reduced and is the oxidant
what are the rules of oxidation numbers
- the oxidation number of any element by itself is 0
- hydrogen has an oxidation number of +1, oxygen has an oxidation number of +2, group 1 = +1, group 2 = +2
- the oxidation number in a monoatomic ion is its charge
- the sum of the oxidation numbers in a compound is 0
- the sum of the oxidation numbers in a polyatomic ion is equal to its charge
what are the exceptions to the oxidation numbers rules
hydrogen has a charge of -1 in metal hydrides, oxygen has a charge of -1 in peroxides and +2 in F2O
permangamante
strong oxidant, MnO4
MnO4
permanganate
dichromate
CrO4, strong oxidant
CrO4
dichromate
