Electrochemistry Flashcards
Equation for Faraday Constant, Avogadro Constant & Charge on Electron
F = Le
E can be found in data booklet (charge of electron)
Steps to determine mass of substance produced at electrode
1) Q = I x t [charge = current x time(s)]
2) charge/96500 = no of mole of electrons
3) use mole ratio to determine mole of substance
4) mole of substance x Mr = mass of substance
Electrolysis: What is the positive and negative terminal and what happens?
Anode:
- positive terminal
- negative ions attracted
- oxidation (loss of e)
- choose ion with more negative value
Cathode:
- negative terminal
- positive ions attracted
- reduction (gain of e)
- choose ion with more positive value
Electrolysis: Molten, what happens at anode and cathode?
Cathode:
- reduction (gain of e)
- positive ions attracted
Anode:
- oxidation (loss of e)
- negative ions attracted
Electrolysis: Aqueous solution, what forms at CATHODE
- can form either metal or H2
- metal below H (positive E) = metal
- metal high above H (negative E) = H2
- metal from Pb to Zn:
- concentrated = metal
- dilute = H2
Electrolysis: What forms at ANODE?
-can form either Halogen or O2
- conc= Halogen
- dilute = O2
Electrolysis: what happens if electrode is NOT INERT
Nothing left on anode but electrode
On cathode, substance will form
Redox Series / Electrode potential
Please stop calling me a careless zebra instead try learning how copper saves gold
K Na Ca Mg Al C Zn Fe Pb H Cu Ag Au
Electrolysis: how to sub in values to determine new e cell when the solution is concentrated or dilute
When equilibrium moves forward, +0.2
When equilibrium moves backward, -0.2
Standard electrode potential
The potential difference of a half cell measured under standard conditions with standard hydrogen electrode as another half cell
Standard Cell Potential
The potential difference between 2 half cella under standard conditions where concentration is 1moldm-3, 298K and 1 atm
Describe Standard Hydrogen Electrode
H2 gas at 1 atm pumped in
Platinum electrode
1moldm-3 and 298K H+
Describe a standard cell
Same conditions as SHE
But with added salt bridge and voltmeter
What happens when the metal is more reactive
Higher tendency to lose e
Undergoes oxidation
Good reducing agent
Equilibrium lies to left
E value is more negative
Equation for total electrode potential
E cell = E reduction - E oxidation
This automatically changes the sign
Only change it if they give oxidation values
How to predict direction of electron flow
Electrons always flow from anode to cathode
Anode= oxidation (more negative E)
Cathode= reduction (more positive E)
Lose e -> gain e
More negative -> more positive
To predict if reaction is feasible
E cell = positive (Feasible)
E cell = negative (Not feasible)
To determine oxidising and reducing agent
More negative E= reducing agent
More positive E = oxidising agent
Effect of concentration on E
If concentration of reactant increases, equilibrium shifts right, E more positive
If concentration of product increases, equilibrium shifts left, E more negative
What is the Nernst Equation used for?
To determine new electrode potential once concentration changes
What does the oxidised and reduced species stand for in Nernst Equation
Oxidised species = the one in higher oxidation state
Reduced species = the one in lower oxidation state
What is the overall equation for all fuel cells?
The combustion equation
Advantages of fuel cells
- Less pollution (no pollutant gases)
- high operating efficiency
- continuously produces electric current
- minimal maintenance
- silent
Disadvantages of Fuel Cell
- costly (catalyst, fuels, oxidants)
- impurities in fuels and oxidants can poison electrode
- high temperature needed
- some electrolytes are very corrosive
