galvanic/fuel cells AOS1 Flashcards
are cells and batteries expensive?
they’re more expensive than energy from other sources like fossil fuels but this cost also allows for greater convenience
what is a galvanic cell?
a galvanic cell (voltaic cell) is a type of electrochemical cell in which chemical energy is converted into electrical energy
what type of reaction occurs in a galvanic cell?
spontaneous and exothermic reactions
what’s an electrochemical cell?
a device in which chemical energy is converted into electrical energy
what’s a battery?
strictly apples to a combination of cells which is done by connecting several cells in a series to obtain a higher potential difference or voltage
what’s an external circuit?
the electric current produced in a cell that flows through the wire and light globe, in a Daniell cell the glob converts the electrical energy of the current into light + heat
what does a flow of current mean?
it means that the chemical reaction (redox) is taking place
what can occur (physically) because of this reaction in a galvanic cell?
in the oxidation half-equation, electrons are lost which prompts corrosion whilst in the reduction half-equation more deposits are added onto it as electrons are gained (sometimes colour loss occurs)
what’s a galvanometer?
an instrument used for detecting electric current (also indicates direction)
what’s a salt bridge?
a salt bridge is used to ensure that current flows between two halves of the cell and is part of the internal circuit of a galvanic cell so it allows a cell to reduce electricity by allowing the movement of ions between the 2 half-cells, preserves electrical connection
what’s a salt bridge made of?
often made from filter paper soaked in a relatively unreactive electrolyte like potassium nitrate (KNO3)
what’s an electrolyte?
a chemical substance that conducts electric current
what’s an oxidising agent?
a chemical that causes another substance to undergo oxidation but it itself is reduced
what’s a reducing agent?
a chemical that causes another substance to be reduced but it undergoes oxidation
how to know if a galvanic cell is spontaneous?
the redox reaction can be described as a spontaneous reaction if it doesn’t need to be driven by an external source of energy (like the reaction occurring naturally)
what happens if reactants are in direct contact with one another?
their chemical energy is transformed directly to thermal energy as opposed to galvanic cells where the half-reactions occur in seperate containers + electrons are transferred by the external circuit so that chemical energy is transformed into electrical energy
how does a galvanic cell work?
half-reactions occur in 2 seperate compartments so since the reductants + oxidants don’t come into direct contact with each other, electrons can only be transferred though an external circuit connecting negative + positive electrodes, this flow of electrons then creates an electric current
what does a half-cell include?
each half-cell contains an electrode in contract with a solution. the species (chemicals) present in each half-cell form a conjugate redox pair
what are the conditions of electrodes?
if 1 member of the conjugate pair in a half-cell is a metal then it’s usually used as the electrode but some redo pairs don’t involve solid metals so if no metal is present an inert (unreactive) elected like platinum/graphite is used but platinum electrodes are very expensive
do half-cells contain other species not involved in the reaction?
yes they do, these include spectator ions and the solvent, if a element is in aqueous form then water is often also present
what happens if 1 of the conjugate pairs in a half-cell is a gas?
then a special ‘gas electrode is used, like a glass of the gas name to prevent it from being lost to the environment
what’s a cathode?
electrode where reduction occurs, electrons are gained, is the positive terminal in a galvanic cell and is where cations in the salt bridge go
what’s an anode?
electrode where oxidation occurs, electrons are lost/ released, negative terminal in a galvanic cell and is where anions in the salt bridge go
what happens in a salt bridge?
it contains ions that move freely between the half-cells so that they can balance changers formed in the 2 compartments
what would happen in a galvanic cell if there wasn’t a salt bridge?
the solution in 1 compartment would accumulate negative charge whilst the solution in the other would accumulate positive charge as the reaction proceeded, this accumulation of charge would stop the reaction very quickly and would prevent further reaction
