Summary Electrochemistry

Electrochemistry:




Zainab Modan

, for assigning
Rules for
Rules numbers ::
oxidation numbers
assigning oxidation
Note to use these rules correctly, it is important that you consider each through in order that it is presented below below
(Each rule takes precedence over any rule that follows it )

↳ Na H → rules 344 take precedence over rule 6
.



.




¥ ¥

1. If any atom in in element form —> ON=zero
2. Monatomic ions—> ON= it’s ionic charge
3. Sum of ON must = total charge on the species
4. Group 1A elements —> +1 ON , Group 2A elements —> +2 ON
5. Fluorine ON = -1
6. Hydrogen ON = +1
7. Oxygen ON = -2
8. Binary compounds with metals, Group 7A elements ON = -1, Group 6A elements ON = -2, Group 5A elements ON= -3


OXIDATION AND REDUCTION
rule ,
-
o +
¥÷+io →
me ,




Zn (s ) + 2 Ht ( aq ) → ZÑ+aq ) + Hz (g)


÷romo-z
F-

Oxidized

A species is oxidized when it loses electrons

A species is reduced when it gains electrons

What is reduced is the oxidizing agent

What is oxidized is the reducing agent
-Oxidation number of an element is the number of electrons that need to be added to the element to make a neutral atom
-Chemical reactions in which the oxidation state of a substance changes are called oxidation-reduction reactions (redox reactions).
•Oxidation involves loss of electrons (OIL).
•Reduction involves gain of electrons (RIG).
Electrochemistry deals with relationships between electricity and chemical reactions.
Oil
Rig
oxidation its Yoss it 7
Reduction is gain
of e-
of e-


Oxidation : Reduction :
-loss of electrons -gain of electrons
-increase in oxidation number -decrease in oxidation number
-when element is oxidised it’s called the Reducing agent because -substance that is reduced is the oxidising agent because causes
it causes reaction to occur in the other element oxidation in opposite substance
-occurs at anode -occurs at the cathode

-both reacts occur simultaneously
-no. Of electrons transferred = no. Of electrons accepted
Zainab Modan

, BALANCING OXIDATION-REDUCTION EQUATIONS
-This involves treating (on paper only) the oxidation and reduction as two separate processes, balancing these half reactions, and
then combining them to attain the balanced equation for the overall reaction


half-reaction method
1. Assign oxidation numbers to determine what is oxidized and what is reduced.
2. Write the oxidation and reduction half-reactions
3. Balance each half-reaction.
a. Balance elements other than H and O.
b. Balance O by adding H2O.
c. Balance H by adding H+.
d. Balance charge by adding electrons

4. Multiply the half-reactions by integers so that the electrons gained and lost are the same.
5. Add the half-reactions, subtracting things that appear on both sides.
6. Make sure the equation is balanced according to mass.
7. Make sure the equation is balanced according to charge.


I
+3


eg.)
¥ t
CZQ?
-




MNOI
M-ritcaqitc-ozcaqsonR.oxid.it#
→
caq ) +
caq ,


-
ON d. Reduced
:




OXIDATION HALF REACTION: Czoc? → 2 coz
-




+ Zé

To balance the carbon, we add a coefficient of 2
To balance the charge, we must add 2 electrons to the right side
.




REDUCTION HALF REACTION:
1. MNOI → Mit The manganese is balanced; to balance the oxygen, we must
add 4 waters to the right side

2. MNOI →
Mn
"
t GHz Oh To balance the hydrogen, we add 8 H+ to
the left side.
-
"

3. 8 Ht + Mnou → Mn + 41420C To balance the charge, we add 5 e− to the
left side
,

, g, , gm.mn , , , mn , ya , ,

To attain the same number of electrons on each side, we
will multiply the first reaction by 5 and the second by 2
COMBINING THE HALF REACTIONS
5 GOI
-




→ LOCO, + loé
"

+ loé + 16 Ht + 2mn05 → 2mn + 8h20


text +5 Czoc?
"
-




toé
-




16 Ht + 2mn04 → 2mn + 8 Hzotlocoz
The only thing that appears on both sides are the electrons. Subtracting them, we are left with:


2mn04 +5 Czoc?
"
-




Hzotlocoz
-




16 Ht + → 2mn + 8


Zainab Modan