Unit 3 Flashcards
Activity
measure of the effective concentration of a species under non-ideal (e.g., concentrated) conditions. This determines the real chemical potential for a real solution rather than an ideal one.
Ionic strength
net effect of the dissolved electrolyte
Formula for ionic strength and define all terms
ionic strength (mu) = (1/2) E c*(z^2)
where E= sigma
c = concentration of ions (make sure to multiply by molar coefficients!)
z = charge (+ or - doesn’t end up mattering)
According to the extended dubeye-huckel equation, as ionic strength increases, the activity coefficient ___
decreases
Formula for activity and define all terms
a = gamma * c
gamma = activity coefficient c = concentration
How does increasing ionic strength affect activity?
decrease
Effective concentration
??? Maybe the actual concentration of species that actually partakes in the chemical reaction
Fill this in:
increase ionic strength = ___ pKa = ___ Ka = ___ solubility
increase ionic strength = decrease pKa = increase Ka = increase solubility
Debye-Huckel Limiting Law and define all terms
log (gamma) = - 0.51 (z^2) sqrt(ionic strength)
gamma = activity coefficient z = charge of species
Extended Debye-Huckel equation and define all terms
log (gamma) = (- A (z^2) sqrt (ionic strength))/(1 + a B sqrt(ionic strength))
gamma =activity coefficient
A and B = temperature dependent constants (should be given)
a = effective diameter of ion (dw about, should be given)
In a galvanic cell, where does oxidation and reduction occur (anode or cathode)
Anode=oxidation, cathode=reduction
What is the purpose of a salt bridge?
- prevent direct mixing of electrolyte solutions
- forces electrons through external circuit
- completes circuit when ions conduct current across the salt bridge
What direction do electrons flow in a galvanic cell?
anode to cathode
True or false: the potential of a cell should never reach zero
False. Reaches zero at equilibrium
In the table of standard potentials, will the values be for oxidation or reduction reactions?
reduction
A positive cell potential corresponds to what type of cell?
Galvanic cell (spontaneous reaction)
A negative cell potential corresponds to what type of cell?
Electrolytic cell (electrical work must be done to drive the chemical reaction)
If you’re only given standard cell potentials for reduction reactions, how do you find the cell potential for oxidation reactions
Just flip the sign (magnitude of cell potential stays the same)
True or false: a standard potential is a measure of the driving force for a reaction from a state of unit activity for reactants and products to their equilibrium concentrations
True. Basically how far away a reaction is from its equilibrium
What does SHE stand for and what is it?
Standard hydrogen electrode. Basically a reference point to compare all other half-cells potentials
What is the SHE standard cell potential?
Assigned cell potential of 0.0
Formula for Nernst equation (at standard condition) and all terms
E=E(naught) - (0.0592/n) ln ([C]^c[D]^d/[A]^a[B]^b)
E(naught)= standard cell potential
n=number of moles of electrons that are transferred
What happens to cell potential when temperature increases?
Cell potential decreases (by looking at full Nernst equation):
E=E(naught) - (RT/nF) ln ([C]^c[D]^d/[A]^a[B]^b)
What is the thermodynamic potential?
Difference between the cathode and anode potential when both written as reductions (look at slides POT #1 slide 40)
