Galvanic Cells as a Source of Energy Flashcards
Describe an electrochemical cell
Device in which chemical energy is converted into electrical energy, or vice versa
Describe a galvanic cell
Electrochemical cell in which chemical energy is converted into electrical energy.
Provide an alternative term to describe a galvanic cell
Voltaic cell
State what a salt bridge is often made from
Filter paper soaked in a relatively unreactive electrolyte (e.g. potassium nitrate solution)
State an early form of the galvanic cell
Daniell Cell
Describe an electrolyte
A chemical substance that conducts electric current as a result of dissociation into positively and negatively charged ions, which migrate toward the negative and positive terminals of an electric circuit.
Describe an electrode
A solid conductor in a half-cell at which oxidation or reduction reactions occur.
Describe electrolysis
Process that produces a non-spontaneous redox reaction by the passage of electrical energy from a power supply through a conducting liquid.
State whether a metal displacement reaction in a Daniell Cell is spontaneous or non-spontaneous
Spontaneous
Describe half-cell
Half of an electrochemical cell.
State what the species present in each half cell forms
A conjugate redox pair
Describe a conjugate redox pair
Oxidising agent and the reducing agent that is formed when the oxidising agent gains electrons
State what half cells usually contain
Other species that are not involved in the reaction (e.g. spectator ions or a solvent)
State the term used to identify the electrode at which oxidation occurs
Anode
State the term used to identify the electrode at which reduction occurs
Cathode
State what terminal the anode of a galvanic cell is considered
Negative
State what terminal the cathode of a galvanic cell is considered
Positive
State the purpose of a salt bridge in a galvanic cell
Contains ions that are free to move so that they can balance charges formed in the two compartments
State to what terminal cations move towards
Cathode
State to what terminal anions move towards
Anode
State what would occur to the conditions within a galvanic cell if a salt bridge was not present
Solution in one compartment - accumulate negative charge
Solution in other compartment - accumulate positive charge
State an alternative term associated with the salt bridge
Internal circuit
State what affect the accumulation of charge in one or both compartments of the galvanic cell (in the absence of a salt bridge) would have on the reaction
Stop reaction and prevent further reaction
State what a metal displacement reaction is an example of
Spontaneous exothermic reaction
State what a metal displacement reaction could be identified as if the reactants are allowed to come into direct contact with one another
Spontaneous exothermic reaction - chemical energy is transformed directly to thermal energy
State whether a metal displacement reaction in a galvanic cell can be classified as a spontaneous exothermic reaction
No. The reactants do not come in contact with one another therefore a chemical-thermal energy transformation cannot occur. (Instead a chemical-electrical transformation occurs).
State what cells and batteries use as their source of energy
Spontaneous redox reactions
State the 2 basic types of cells
- Primary cells - disposable and designed not to be recharged
- Secondary cells - rechargeable and designed to be reused many times
State what both primary and secondary cells can be classified as
Galvanic cells
State whether commercial alkaline cells are considered rechargeable or non-rechargeable cells
Non-rechargeable cells
State what must occur for commercial alkaline cells to ‘go flat’
Reaction reaches equillibrium
State what cells that cannot be recharged are considered
Primary cells
State what cells that are designed to be recharged are considered
Secondary cells
Provide 2 examples of rechargeable cells
- Lithium-ion cells
2. Nickel-metal hydride cells
State whether lithium-ion cells and nickel-metal hydride cells are considered rechargeable or non-rechargeable
Rechargeable cells
State how a rechargeable cell is recharged
Cell reaction must occur in reverse (the products of the reaction must be converted back into the original reactants)
State to which electrode of a rechargeable battery the positive terminal of a charger is connected to
Positive electrode
State to which electrode of a rechargeable battery the negative terminal of a charger is connected to
Negative electrode
State what electrical energy supplied by the charger is converted into
Chemical energy in the cell
State what must occur in order to regenerate the reactants of a rechargeable cell
Products formed in the cell during discharge must remain in contact with the electrodes in a convertible form
State where oxidation occurs during the discharging process within a secondary cell
Anode (negative terminal)
State where reduction occurs during the discharging process within a secondary cell
Cathode (positive terminal)
State where oxidation occurs during the recharging process within a secondary cell
Anode (positive terminal)
State where reduction occurs during the recharging process within a secondary cell
Cathode (negative terminal)
State the general trend that occurs when a secondary cells is recharged
Reactions are reversed at each electrode
State a reason supporting the limited life of batteries
Unwanted physical and chemical changes that occur within them
State what deteriorates at each charge-discharge cycle
Battery performance
State what the term battery life describes
Number of charge-discharge cycles that occur before a battery becomes unusable
Provide 6 factors which influence battery performance over time
- Loss of active materials
- Conversion of active material at electrodes
- Formation of other chemicals in side reactions
- Impurities
- Electrolyte-electrode contact
- Corrosion/failure of internal components
Describe how active material may be lost to influence battery performance
Detachment of active material from the electrode on each cycle
Describe active material
Reactants and products of the cell reaction
Describe progressive conversion of small crystals of active material at the electrodes as a factor influencing battery performance
Progressive conversion of small crystals of active material at the electrodes into larger crystals at each cycle - increases resistance to current flow
Describe formation of other chemicals in side reactions as a factor influencing battery performance
Formation of other chemical in side reactions - impede the efficient functioning of the cell
Describe impurities in cell materials as a factor influencing battery performance
Impurities in cell materials (including electrodes) - may react with active materials
Describe how electrolyte-electrode contact may decrease within a battery
Leakage of electrolyte
or transformation into non-conductive material
Outline the relationship between battery performance and temperature
The higher the temperature, the higher the rate of battery deterioration
State what batteries release under normal operation
Heat energy
State what occurs when battery operating temperature rises
The rate of the side reactions increase and the battery life becomes shorter
State whether lithium-ion or nickel-metal hydride batteries are more sensitive to the effect of heat
Nickel-metal hydride batteries
State what occurs when batteries operate under cold conditions
Battery capacity decreases
State why battery capacity decreases when batteries operate under cold conditions
Reactions rate fall as temp decreases
Therefore, batteries deliver less electric charge at specific discharge rates under cold conditions
Summarise the effect of temperature on battery life/performance
Cold conditions - decrease battery performance
Warm conditions - decrease battery life
State whether or not side reactions and deterioration continue even when batteries are not in use
Yes.
Describe self-discharge
Continuation of side reactions/deterioration of battery even when not in use
State how battery life can be extended when it is not in use
Storage at low temperature (which slow side reactions)
