Transcript Unit 13 - Electrochemistry

Unit 13, Ch. 22 –
Redox Reactions
Vocab Oxidation
Loss of eGain of oxygen
Oxidation Is Losing e-
Reduction
Gain of eLoss of oxygen
Reduction Is Gaining e-
Oxidation – reduction reaction: Any chemical change
in which one compound is oxidized (loses electrons)
and another compound is reduced (gains electrons);
also called a redox reaction.
Mg + S →
2+
Mg
+
2S
Loses e-s magnesium atom is said to be oxidized to a magnesium ion
Sulfur atom gains two e-s and is reduced to a sulfide ion
Oxidation : Mg → Mg2+ + 2eReduction: S + 2e- → S2-
(loss of electrons)
(gain of electrons)
Half- Reactions: shows either reduction or oxidation, but not both.
Only the species of atom that is involved in the change
Sample Prob 22-1 remember that individual atoms and compounds are
neutral (have no charge)
2AgNO3(aq) + Cu(s) → Cu(NO3)2(aq) + 2Ag(s)
Practice Assigning Oxidation #s
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Use the oxidation numbers to identify which
atoms are oxidized and which are reduced in
each reaction.
a. Cl2(g) + 2HBr(aq) → 2HCl(aq) + Br2(l)
b. C(s) + O2(g) → CO2(g)
c. Zn(s) + 2MnO2(s) + 2NH4Cl(aq) →
ZnCl2(aq) + Mn2O3(s) + 2NH3(g) + H2O(l)
- The substance that is oxidized is called
the reducing agent.
 - The substance that is reduced is called
the oxidizing agent.
 - Single replacement and combustion
reactions are redox reactions, double
replacement is not a redox reaction.
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Electrochemistry: The branch of chemistry that is the study of
the relationship between electric forces and chemical reactions.
Voltage: The potential difference or electromotive force,
measured in volts; it represents the amount of work that moving
an electric charge between two points would take.
Electrode: A conductor used to establish electrical contact with
a nonmetallic part of a circuit, such as an electrolyte.
electrochemical cell: A system that contains two electrodes
separated by an electrolyte phase.
Cathode: The electrode on whose surface reduction takes
place.
Anode: The electrode on whose surface oxidation takes place;
anions migrate toward the anode, and electrons leave the
system from the anode.