POM: Energy from Redox Reactions Flashcards
What is a displacement reaction?
A displacement reaction is really an oxidation-reduction reaction involving a transfer of electrons.
Identify the relationship between the displacement of metal ions in solution by other metals to the relative activity of metals
A spontaneous redox reaction will occur if the reductant is higher in the tbale of standard reduction potentials thn the oxidant.
The further apart the ions are, the more vigorous the displacement reaction (and thus more energy released)
What are the rules for oxidation states?
Elemental form = 0
Neutral molecules = 0
Monatomic ions have oxidation numbers equal to their charge
Polyatomic (eg) Po4) have number equal to their charge
Oxygen = -2 Hydrogen = -1
Account for changes in the oxidation state of species in terms of their loss or gain of electrons.
Oxidation involves an increase in oxidation state.
Reduction involves a decrease in oxidation state.
What is a galvanic cell?
A galvanic cell involves separating the oxidation and reduction reactions of a redox reaction into two separate half-cells, connected by a conductive wire and salt bridge.
This arrangement ensures that electrons cannot go directly from the reductant to the oxidant, but they will move through the external circuit
Define the terms anode, cathode, electrode and electrolyte to describe galvanic cells
Anode - The anode is the electrode that releases electrons at which oxidation occurs
Cathode - The cathode is the electrode that receives electrons at which reduction occurs
Electrode - The conductors of a cell which get connected to the external circuit
Electrolyte - A solution that releases ions when in solution and that carries an electric current. It is required for ions to move through the internal circuit.
What isthe purpose of a salt bridge?
The salt bridge (KNO3) is the ion path between half cells which keeps the electrical balance in the cell. This prevents the build up of positive charge at the anode and negative charge at the cathode.
Why might there be a variation in standard potentials recorded from experiment?
Bench voltmeters have a relatively low resistance which means that they create a load on the galvanic cell, resulting in a voltage drop according to Ohm’s Law. It would be better to use a digital multimeter, which results in much lower voltage drops.
Standard potentials are measured with solutions of 1 molL-1 with gases at a pressure of 1 atmosphere, and at standard conditions temperature of 25°C. The experiment conducted does not follow the same, as the solutions are imperfect as the water is not deionised and may have been involved in cross contamination. Also the school laboratory’s temperature is not 25 degrees or constant, therefore causing a variation in the results
What is the anode, cathode and electrolyte.of a dry cell?
The anode is a zinc container, and the cathode is a carbon rod surrounded by a layer of ammonium chloride and manganse dioxide paste
The electrolyte is a paste containing ammonium chloride and zinc chloride
What is the cost and practicality of a dry cell?
Materials of the cell are inexpensive and cheap to replace even though the cell is non-rechargeable.
Low energy density
Short life - the zinc is attacked by the ammonium chloride.
The zinc casing oxides during cell discharge, and the acidic paste can leak out through cracks and corrode other components
What is a dry cells impact on society?
Used in low-drain appliances such a torches, remote controls, LCD calculators, and battery-powered toys that do not require high currents
What is a dry cells environmental impact?
Battery components are weakly acidic and non-toxic
Few environmental consequences on disposal
What is the anode, cathode and electrolyte of a button cell?
Anode: powdered zinc
Cathode: Carbon and AgO paste or mercury
Electrolyte: Potassium hydroxide
What is the cost and practicality of a button cell?
Expensive due to the high cost of silver
Non-rechargeable, so it should be recycled rather than discarded so that the silver can be recovered
Long shelf life
What is a dry cells impact on society?
Widely used in watches, cameras, hearing aids, or other appliances that require a small battery that produces a stable voltage over the batter’s life.
