5E - Redox definitions Flashcards
Reduction
- Gain of electrons
- Decrease in oxidation number
Oxidation
- Loss of electrons
- Increase in oxidation number
Oxidising agent
Reagent that accepts electrons from another speies (it itself is reduced)
Reducing agent
Reagent that donates electrons to species being reduced (it itself is oxidised)
Redox reaction
Reaction involving oxidation and reduction
Disproportionation
Redox reaction in whcih the same element is both oxidised and reduced
Oxidation number
A measure of the number of electrons that an atom ises to bond with atoms of another element:
- Uncombined elements = 0
- Group 1 elements = +1
- Group 2 elements = +2
- Fluorine = -1
- Oxygen = -2 unless it’s in a peroxide in which case it’s -1
- Hydrogen = +1 unless it’s in a hydride in which case it’s -1
Half cell
Contains an element in 2 different oxidation states together with a means of electrical contact (e.g. a piece of metal)
Salt bridge
A concentrated solution of an electrolyte that doesn’t react with the materials in either half cells to complete the circuit by allowing ions to flow between the half cells
e.g. piece of filter paper saturated in KNO3(aq)
Standard electrode potential (E⦵)
The emf of a half cell compared with a standard hydrogen half cell, measured at:
- Temperature of 298 K
- Solution concentrations of 1 moldm-3
- Gas pressure of 100 kPa
Equation for E⦵(cell)
E⦵(cell) = E⦵(more positive electrode) - E⦵(more negative electrode)
E⦵ value > 0 (feasible reaction)
E⦵ value < 0 (not feasible reaction)
Storage cell (4)
- Often known as a battery.
- Has a fixed amount of chemicals which are used up as the cell discharges and its energy is used
- Has a specific amount of energy it can supply
- Depending on the cell, it may be able to be recharged
Fuel cell (3)
- Uses a fuel + oxygen which undergo an exothermic reaction
- Reaction arranged so that energy produced is electrical energy
- Fuel can continue to operate as long as furl and oxygen are available
