Electrochemistry

What is a reducing agent?

Causes another atom to gain electrons

Gets oxidized

What is an oxidizing agent?

Causes another atom to lose electrons

Gets reduced

What does oxidation mean?

Loss of electrons

What does reduction mean?

Gain of electrons

How is electric current calculated?

I = q/s

I = current

q = charge in Coulombs

s = seconds

How is power calculated?

P = EI

E = voltage

I = current

How is delta G found?

Delta G = -nFE

n = mol electrons

F = Faraday’s constant

E = voltage

What is the reaction of a mercury cell?

Zn(s) + HgO(s) ←→ ZnO(s) + Hg(l) E^o = 1.35V

How do you draw a Galvanic cell?

Anode: where oxidation occurs; -

Cathode: where reduction occurs; +

Salt bridge connects them

Voltage measured

How is cell notation written?

Electrode | solid | electrolyte || electrolyte | solid | electrode

Oxidation half-cell || reduction half cell

What direction do electrons flow in a galvanic cell? Ions?

From anode to cathode

Ions flow opposite

How is oxidation number assigned?

1. Elements have 0

2. H is + 1

3. O has -2

4. For monoatomic ions, oxidation = net charge

5. Alkali metals +1

6. Alkaline earth metals +2

7. Halogens -1 unless combined with:

   1. F is -1

   2. Bount to eachother

   3. Bound to more than one atom

   4. Bound to oxygen

8. Sum of oxidation states = net charge of atom

How is direction of electron flow found?

From anode to cathode

Balance electrons in half reactions to determine

How are reactions balanced?

1. Assign oxidaiton states

2. Write half cell reactions

3. Balance each half reaction

   1. Balance atoms except O and H

   2. Add H2O to side lacking O and balance

   3. Balance H by adding H+

4. Balance electrons

   1. Add electrons to product side for oxidation

   2. Add electrons to reactant side for reduction

5. Balance electrons between half cells

6. Add half reactions and cancel common

7. Check numbers of atoms are equal

8. In basic solution, neutralize H+ with OH-

What is standard electrode potential for Ag?

Reduced against SHE

Ag+ + e- ←→ AG

E^o = 0.7993 V

What is standard electrode potential of Cu against SHE?

Cu2+ + 2e- ←→ Cu

E^o = 0.34 V

What is standard electrode potential of Zn against SHE?

Zn 2+ + 2e- ←→ Zn

E^o = 0.76 V

What is reduction potential?

How likely something is to get reduced

Higher = more likely = electrons flow towards it = cathode

What is the cell potential equation?

E^o_cell = E^o_cathode - E^o_anode

Cathode always has greater reduction potential

How is half cell potential determined?

E = E^o + 0.0592/n log Q

At 25 C

E = E^o - RT/nF ln Q

R = 8.314 (VC)/(K/mol)

T = temperature in K

n = number moles electrons

F = 96485 C/mol e-

Q is like equilibrium constant, but not at equilibrium

What are conditions of standard cell potential?

1 atm

25 C

1 M solution

What is standard hydrogen electrode?

2H+ + 2e ←→ H2

E^o = 0.000V

At standard conditions

What is the nernst equation?

E = E⁰ - RT/nF ln Q = E^o -0.0592/n log Q

How is K found from nernst equation?

K = 10^{nE^o / 0.0592}

How does E relate to direction of electron flow?

Electrons flow from lower to higher E