Batteries Flashcards
(35 cards)
What is the purpose of a battery?
To store energy in electrochemical form and release that energy on demand.
Define a redox reaction.
A type of chemical reaction where the reactions are either reduced or oxidized by gaining or losing electrons (respectively).
Which electrode does oxidation occur at in a galvanic cell?
Anode (remember: AnOx)
Which electrode does reduction occur at in a galvanic cell?
Cathode (remember: RedCat)
Which is the difference between a cell and a battery?
A cell is the smallest individual electrochemical storage unit. A battery is a group of cells connected together to form a larger storage unit.
In what ways can cells be connected to form a battery?
Either in series or in parallel
What is the difference between a primary and secondary cell? What is a secondary cell often termed?
Primary cells are single discharge, secondary cells can be recharged and discharged multiple times. Secondary cells are often called ‘rechargeable.’
When a galvanic cell discharges, electrons are removed from the cathode and released into the anode. How does the cell still stay electrically neutral?
Charged species are drawn across the electrolyte/salt bridge to balance out the movement of charge.
What is the relationship between a spontaneous reaction and Gibb’s free energy?
If the change in Gibb’s free energy is negative for a reaction, that reaction will be spontaneous.
True or False: ΔrG = ΣΔG(products) - ΣΔG(reactants)
True
True or False: ΔrG = ΣΔG(reactants) - ΣΔG(products)
False
True or False: E(cell) = E(red) + E(ox)
True
How can we tell where the energy of a cell is stored?
If | Δmetal G | > | Δion G | then more energy is stored as “lattice cohesive energy”, rather than “ionization energy of metal atoms in water.” Vice versa.
What is the energy transformation that occurs during the discharge of a galvanic cell?
Chemical energy -> electrical energy
What type of system is a battery?
Close system (mass and charged conserved, energy transfer through system boundary)
A battery will be labelled with its ‘nominal voltage’ and ‘nominal capacity’. In these cases, what does ‘nominal’ mean?
Average or typical
A battery will be labelled with its ‘nominal capacity’. Give the definition and the units for this quantity.
It is the (average) steady quantity of charge the battery can release over an hour. It is the integral of current with respect to time. Typical units are ampere hours (Ah).
What are three factors that the voltage of a battery depends on?
Internal resistance of battery, chemical components, arrangement of cells (i.e. series or parallel).
What component of a cell is often called a ‘charge reservoir’?
Electode
Fill in the blank:
A cell inside a rechargeable battery is similar to a galvanic cell, but the salt bridge is replaced with a _____ _____.
Electrolyte solution
What electrolyte is used in a PbA (lead acid) battery? Which species inside the cell is reduced when the battery discharges? Which is oxidised?
Electrolyte = dilute sulfuric acid. Pb4+ ions (part of the PbO2 lattice) are reduced. Pb(s) atoms are oxidised.
When a PbA battery discharges, there is a movement of electrons across each cell. How does conservation of charge still hold true across the cell?
Movement of charged ions inside the electrolyte solution (H+ and HSO4 -)
Discuss the movement of electrons at each anode of a PbA cell.
Pb (s) anode releases electrons and so is oxidised. PbO2 cathode accepts electrons and is reduced. Oppose of both is true when battery is recharged.
What electrical properties does a separator have in a PbA cell? State a couple of examples of suitable materials.
Electrical insulator. Examples: glass mats, plastic polymers usually
