Chapter 20 Flashcards
Anode half reactions go from?
solid to aq
Cathode half reactions go from?
aq to solid
How to Balance Redox Reactions in Basic Solution?
- Assign oxidation states
- Write two half reactions
- Balance all atoms except for H and O
- Balance O atoms by adding H2O and balance H atoms by adding H+ (aq)
4b. For every H+ atom added, add an OH- atom to BOTH sides of the reaction.
4c. Combine the H+ and OH- atoms occurring on both sides of the equation to form H2O - Balance the charge of both half reactions by adding electrons.
- Equalize the electrons in both half reactions.
- Add the two equations to make an overall reaction.
How to Balance Redox Reactions in Acidic Solution?
- Assign oxidation states
- Write two half reactions
- Balance all atoms except for H and O
- Balance O atoms by adding H2O and balance H atoms by adding H+ (aq)
- Balance the charge of both half reactions by adding electrons.
- Equalize the electrons in both half reactions.
- Add the two equations to make an overall reaction.
How to label a voltaic (or galvanic) cell:
Electrons move from the cathode to the anode.
At the anode, the element is being oxidized (losing electrons). Labeled with a negative (-) sign.
At the cathode, the element is being reduced (gaining electrons). Labeled with a positive (+) sign.
The salt bridge provides more protons to the cathode and more electrons to the anode.
1 Ampere (or amp) =
1 C/s
1 Volt (V) =
1 J/ C
E cell is…
(definition)
cell potential or cell emf
E cell Naught is…
(definition)
The standard cell potential or standard emf
A double vertical line in electrochemical cell notation means…
the separation between the two-half reactions
The equation for E cell naught for cathode and anode is…
E0= E0 final- E0 initial
E0= E0cathode- E0anode
E0= E0cath- E0ano
The reaction is nonspontaneous if the E0 is?
Negative
The reaction is spontaneous if the E0 is?
Positive
The reaction is spontaneous if the reduction half reaction is paired with?
the REVERSE of any equation listed below it. on the table
Ex. F2(g) +2e- —> 2F- (aq) [at the top of the list] is spontaneous with reverse of Br2(l)+ 2e- —> 2Br- (aq) [12 spots below fluorine]
For a spontaneous redox reaction, ΔG0 is _____, E0cell is _______, and K is _____ _____ 1.
ΔG0 is negative
E0cell is positive
K is greater than 1
For a nonspontaneous redox reaction, ΔG0 is _____, E0cell is _______, and K is _____ _____ 1.
ΔG0 is positive
E0cell is negative
K is less than 1
Equation between ΔG and E0:
ΔG0= -nFE0cell
ΔG0 is the standard change in free energy
n-moles of electrons in the BALANCED equation
F is Faraday’s constant
What is the value of Faraday’s constant, F?
96485 C/ mol e-
Equation between E0 cell and K:
E0 cell= (0.0257/n) lnK
Equation of E0cell involving R, T ,n ,F, and K?
E0cell= (RT/nF)lnK
R- 8.314 (J/molK)
F- 96485 (C/mol e-)
What is the Nernst Equation at standard conditions?
E cell= E0 cell- (0.0257 V/ n)* lnK
What is the Nernst equation at nonstandard conditions?
E cell= E0cell- (0.0257V/n)(ln Q)
If half reactions are identical (where one is in the fwd direction and one is in the reverse), the STANDARD CELL POTENTIAL is…
E0cell= 0
In voltaic cells, the cathode is ____ charged and the anode is ____ charged.
positively (+)
negatively (-)
