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To design an electrochemical cell that produces an optimal energy output. …
To design an electrochemical cell that produces an optimal energy output.
What are electrochemical cells/types?
Type of cell: galvanic/voltaic or electrolytic.
Galvanic cells transform the chemical potential energy of chemical reactions into electrical energy.
Involves the transformation between electrical and chemical energy.
Electrolytic cells use electrical energy to generate chemical reactions (via electrolysis).
What kind of energy output do electrochemical cells have?
Galvanic cells can use the chemical energy of spontaneous redox reactions to generate electrical energy which can be used in daily life.
Electrolytic cells use an external source of electrical energy to drive a non-spontaneous chemical reaction. They can be used to decompose compounds into their constituents.
Electrochemical cells use one form of energy and convert it into a more useful form, depending on what is required.
What indicates an 'optimal energy output'?
High amounts of electric current being produced in a galvanic cell.
High potential difference/voltage between anode and cathode which leads to greater electricity generation.
Greatest rate of the chemical reaction required in an electrolytic cell.
What are the components of a galvanic cell and how does it work?
Has two metal electrodes (half-cells): anode (-) and cathode (+).
A salt bridge which connects the electrodes and carries charge.
Two electrolyte solutions which act as charge balancers due to the free ions they contain.
Oxidation occurs at the anode, which transfers electron to the cathode, where reduction occurs.
Can be used as a battery where many cells are lined parallel to one another in order to generate electricity.
Are used as fuel cells which generate large amounts of electricity from spontaneous redox reactions to power large appliances.
What are the components of an electrolytic cell and how does it work?
Has two metal electrodes: anode (+) and cathode (-).
Both electrodes are dipped into the one electrolyte solution.
Non-spontaneous redox reaction is initiated by an external source of electrical energy, such as an external battery.
External battery supplies electrons, which enter through the cathode and exit through the anode.
Used to decompose a compound into its constituents via a non-spontaneous redox reaction.
Electrolysis is the process often used, which passes an electric current through a compound to induce a chemical change, such as breaking down sodium chloride into sodium and chloride.
How can 'optimal energy output' be measured?
A voltmeter can be connected in the circuit to measure the voltage of the current generated in a galvanic cell.
An ammeter can be connected in the circuit to measure the how much current is generated in a galvanic cell, or a bulb can be connected in circuit of a galvanic cell and it can be observed how bright it shines to determine the strength of the current produced.
A cell must be long-lasting: a bulb can be connected in circuit and it can be seen how long it shines for in a galvanic cell.
Suitable electrodes, electrolyte solutions and salt bridges
Cathode: Must be a good oxidising agent as reduction occurs here. Therefore, a relatively non-reactive metal is required, such as copper (Cu), silver (Ag), etc.
Anode: Must be a good reducing agent as oxidation occurs here. Therefore, a relatively reactive metal is required, such as magnesium (Mg), zinc (Zn), lithium (Li), etc.
Electrolyte solutions: Usually the sulphates of the metal electrodes, which will ionise in water easily and produce free ions that can act as charge balancers. They should not react with the metal itself and form precipitates which is why the respective metal sulphates are used.
Salt bridge: Acts as a charge carrier and needs to be an electrolyte solution which will dissociate easily in water to carry current properly, such as: sodium chloride, potassium nitrate, etc.
A salt bridge can be constructed by dipping some filter paper or string into the salt solution and connecting it with the vessels containing the electrodes.
Benefits of electrochemical cells
Can be constructed easily using lab equipment.
Unlimited access to materials needed.
Long-lasting/durable with fixed current and portable.
Rechargeable and lightweight.
Limitations of electrochemical cells
Rusting and physucal damage of half-cells becomes blatant overtime, causing chemical leaks which are hjazardous
Voltage becomes unstable as battery age grows and becomes unreliable,
To power a large fuel cell, continuous recharging and unlimited resources are needed which are impractical in the real-word of finite resources.
Conditions required for an effective electrochemical cell
Metal reactivity is determined using the metal reactivity series which orders them in ascending order based on their ability to be oxidised, The highly reactive metals lie towards the top, acting as effective anodes (high ability to be oxidised) and the highly non-reactive metals lie towards the bottom, acting as effective cathodes (high ability to be reduced).
Optimal temperature, since it affects the voltage of the half-cells, which affects the current and the energy output.
Concentration of electrolyte solutions and salt bridge affects the transfer of electrons, current generated and energy output.
Anode and cathode reactivities affect the voltage: the greater the potential difference between the electrodes, the higher the voltage and the greater the current generated.