Lecture 1 Flashcards
What is electrochemsitry?
the study of the relationship between electricity and chemical change
What is a redox reaction?
oxidation and reduction both occurring
What substance acts as the oxidising agent?
the substance that has been reduced acts as the oxidising agent
How do construct a half equation?
- put in the species thats being changed
- Balance H using H+
- Balance O using water
- Balance charge using electrons
What are the 2 half equations for the oxidation of hydrogen?
H2 oxidation;
2H2 = 4H+ + 4e
O2 reduction;
O2 + 4e + 4H+ = 2H2O
What are the applications for fuel cells in energy tech?
- energy release e.g. H2 powered vehicles
- electrons flowing through the circuit can be made to do electrical work e.g. powering a motor
- Energy capture e.g. ‘Artifical leaf’ chemical copy of photosynthesis, converting light energy of sun into stored chemical energy of a fuel molecule
What are the applications of fuel cells in chemical synthesis?
- use an electrical driving force to activate otherwise challenging chemical bond formation reactions
e.g. C-H bond activation
Define anode and cathode
Anode= where oxidation occurs
Cathode= where reduction occurs
What is the cell voltage equation?
Ecell= Ecathode - Eanode
What is a discharging battery?
discharging battery means electrical energy is being produced, the opposite of a recharging battery
Draw the cell diagram for copper-zinc battery
See pg 14 of handout
Give the equation for ^Gcell
^G = -nFEcell
n= number of electrons transferred
F= farraday constant
Ecell=cell potential
gives answer in Jmol-1
Give the equation for ^G using equilibrium constant
^G= -RTlnK
K= e^-G/RT
Explain the terms ‘standard electrode potential’/ ‘standard reduction potential’/ ‘standard midpoint potential’
To quantify the thermodynamics of the reversible reduction/oxidiation of a substance we define these values, often denoted E, which are the measure of the individual potential of a reversible electrode under standard conditions
What are the standard conditions?
- stated temp usually 298K
- 1 moldm-3
- 1 atm
- metals in their pure state e.g. not alloys
How is a standard electrode potential measured?
Standard electrode potentials are defined relative to the standard hydorgen electrode;
2H+ + 2e = H2 which has a E value of 0 V.
How do you know if a reaction is spontaneous?
negative ^G
What is the equation for ^G reaction?
^G = G oxidation + G reduction
How do ^G and Ecell link?
Battery operating in discharge mode has ^Gcell < 0 because spontaneous flow of electrons
so Ecell is positive (Ecathode > Eanode)
