lecture 7: fundamentals of electrochemistry Flashcards
(26 cards)
What is a redox reaction?
transfer of electrons from one reagent to another reagent
What are the rules for oxidation states?
- oxidation state of an atom in an element is 0 (Na (s), O2(g)
- oxidation state of monatomic element: its charge (Na+ = +1)
- oxygen = -2 in covalent compounds: CO, CO2
- H = +1 in covalent compounds wiht nonmetals: HCl, NH3
- Fluorine= -1
What is oxidation?
a chemical change in which an atom loses an electron
What is reduction?
a chemical change in which an atom gains an electron
What is a reducing agent?
substance that supplies electrons and causes reduction in another substance (oxidizing itself to reduce smt else)
What is an oxidizing agent?
substance being reduced and acquiring electrons from another substance (oxidizing smt else to reduce itself)
What is the formula for balancing by half-reaction method in acidic medium?
- assign oxidation states for each element
- write separate reduction and oxidation reactions
- balance elements (except for H and O)
- balance O with H2O
- balance H with H+
- balance charge with electrons
- multiply by an integer to equalize electron count
- add half-reactions and cancel
- check if everything is balanced
What is the formula for balancing by half-reaction method in basic
- assign oxidation states for each element
- write separate reduction and oxidation reactions
- balance elements (except for H and O)
- balance O with H2O
- balance H with H+
- balance charge with electrons
- multiply by an integer to equalize electron count
- add half-reactions and cancel
- add OH to equal the amount of H+
- Form water by combining H+ and OH-
- check if everything is balanced
What is an electric charge?
it is a measurable property of the electrons that are transferred in a redox reaction (measured in coulombs)
How do you calculate the total charge of an ion?
q = n x N x F
q = charge in coulombs
n = unit charges per molecule
N = moles
F = faradays constant
What is electric current?
the quantity of charge flowing each second through a circuit (measured in ampere A)
How is current related to rate of reaction?
current = charge/time = coulumbs/second = moles e-/second x coulombs/mole (C/s = A)
What is the electric potential difference?
E, between two points is the work required or which can be done when a unit charge moves from one point to the other measured in V
What is the relation between work, voltage and charge?
Work (in joules) = E (V) x q (C)
1V = 1 J/C
What is a galvanic cell?
it uses spontaneous redox reaction to generate electricity (like a battery). electrons flow from anode to cathode, with oxidation occuring at the anode.
What is a salt bridge?
It is a U-shaped tube filled with a gel containing an electrolytw not involved in the reaction.
How is the line notation made for galvanic cells?
Anode|components in oxidation||components in reduction |cathode
How is cell potential measured?
the potentiometer measures the difference in electric charge between two metal electrodes: E = E+ - E-
How is the standard cell potential calculated?
Standard cell potential = Eºcell
Eºcell = SRP of metal being reduced (E+) - SRP of metal being oxidized (E-)
if positive = spontaneous
The values with the lowest standard cell potential are…?
Best reducing agent, get oxidized
the values with the highest standard cell potential are…?
best oxidizing agent, easiest to reduce
What is the nernest equation and what is it used to calculate?
used to calculate the reduction potential for each half-cell
E = Eº - RT/nF lnQ
What are reference electrodes?
half-cell with a fixed composition so it has a constant potential
What is an indicator electrode?
electrode that responds to the analyte activity
