Chapter 20: Electrochemistry Flashcards
Electrolysis
Decomposition of a compound into its elements by an electric current
Electrolyte
Compound that is decomposed either molten ionic compound or conc aq solution of ions
Electrodes
Rods of carbon(graphite)/metal conduct electricity to and from an electrolyte
Redox at cathode
Gain electrons, always reduction, metal layer or molten layer in the cell, gas bubbles off
Redox at the anodes
Anions. Lose electrons. Oxidize.
Mass of substance proportionality
Strength of current and time over which a constant electric current passes
Faraday definition
Quantity of electricity charge carried by 1 mol of electrons or singly charged ions.
Faraday value
96 500 C mol^-1
Steps to calculate mass using F
Write half-equation
Find number of electrons E, multiply by F
Calculate Q=It
Calculate M = Q/ EF * Ar
Calculating volume(at rtp)
Write half-equation
Find number of electrons E, multiply by F
Calculate Q=It
Calculate M = Q/ EF * 24.0
Avogadro constant
L= F/C
Redox equilibrium
Exists between 2 chemically related species that are in different oxidation states
Rate of electrons = rate of electron loss
Finding the charge on 1 mole of electrons steps
Weigh the electrodes separately
Pass constant current over period of time
Remove, wash and dry electrodes with distilled water and propanone
Reweigh electrodes: cathode increases, anode decreases
Calculation for finding the charge on 1 mol of electrons
Mass of anode at the start and end Mass removed at anode Charge transfer Calculate 1 mol in grams of substance Mole/weight x charge =X How many electrons for one mole= Y X x Y = Z L = Z/electrons
Electric potential(voltage)
The relationship established when a metal is put into a solution of its own ions, between the metal and metal ion system in solution
Electrons Potential E
Difference between 2 systems
Cannot be measured because of electrical double layer when an element is placed in a solution of its ions
Standard cell potential
E cathode - E anode
Flow of electrons using E standard
More positive pole attracts the negative electrons
Predicting reaction using E standard
More positive, forward direction, easier to reduce
Less positive, reverse direction, easier to oxidize
Feasibility
Feasible if likely to occur, standard cell potential value is positive, forward reaction is feasible not reverse, doesn’t determine rate
Direction of reaction
Clockwise pattern
More positive to less positive: reactant to product of more positive to reactant and product of less positive
Will It oxidize?
- Write half reactions(more positive on top)
- Identify stronger oxidizing and reduction agent: more positive is oxi because more likely to accept. Less positive is red, more likely to release
- Do they react
- More positive reaction goes forward, less positive goes reverse
- Combine half-equations
Why is platinum used in the standard hydrogen electrode
Inert, doesn’t take part in the reaction, surface allows electron transfer from one species to another, ensures electrical contact
What do E standard values represent
Indicates how easy it is to reduce or oxidize