# Redox Reactions Worksheet II ```Redox Reaction Worksheet
Vocabulary
Electrochemical Cell (voltaic cell, galvanic cell,
battery)
Electrode
Anode
Redox reaction
Cathode
Redox couple
Standard cell potential (Eocell)
Half-reaction
Volt (1 J/C)
Half-cell
Standard reduction potential (Eored)
Introduction
Redox reactions involve electron transfer between species, causing changes in their oxidation states. We
usually talk of redox couples such as Zn / Zn2+ and Fe2+ / Fe3+ (reduced form / oxidized form) when
characterizing redox reactions. (Recall the half-reaction method of balancing redox equations). In this
exercise we deal with electrochemical cells, in which two redox couples are placed in separate
compartments as opposed to their direct contact.
Cell potential
The cell voltage is a measure of the potential energy difference between the two electrodes so it is also
called cell potential. A potential difference of 1 volt (V) is sufficient to impart 1 J of energy to a charge
of 1 coulomb (C) (In other words: 1 V = 1 J/C). Cell potential is the driving force for a redox reaction so
it is also called electromotive force (emf, E). It is a measure of how far a redox reaction is from
that is
occurring!
Gravitational Potential Energy
Cell Potential
Although we can only measure differences in
potential, a number called the standard
reduction potential (Eored or simply Eo ) can
be assigned to every half-reaction by assigning
a value of zero to a reference half-reaction.
The reference half-reaction is:
2H+(aq) + 2e- → H2 (g) Eo = 0 V
Reductions that occur more easily than this
one are given a positive Eored. Reductions that
occur less easily have a negative Eored.
1
2
The standard cell potential for any cell can be calculated as the difference between the standard reduction
potentials for the reactions occurring at the two electrodes.
Eocell = Eocathode - Eoanode
(Some textbooks use the symbol Eo instead of Eocell.)
Zinc-Copper Cell: Zn/Zn2+ ‫ ׀׀‬Cu/Cu2+
red wire
Overall cell reaction: Zn(s) + Cu2+(aq) → Zn2+(aq) + Cu(s)
3
Memory tricks
Oxidation takes place at the Anode (vowels!)
Reduction takes place at the Cathode (consonants! Red wire!)
Cathode and Cations are +; Anode and Anions are Cations are attracted to the Cathode
Anions are attracted to the Anode
Standard Hydrogen Electrode (SHE)
Practice Problems:
1. For the complete combustion reaction of propane gas (C3H8):
a. Write the proper presentation of this chemical change.
b. Identify whether this reaction is a redox reaction.
c. Identify the oxidizing and reducing agents.
2. When iron is immersed in copper(II) chloride aqueous solution:
a. Write the proper presentation of this chemical change.
b. Identify whether this reaction is a redox reaction.
c. Identify the oxidizing and reducing agents.
d. Used the standard reduction potential for half-cells to justify your answer.
e. To utilize this reaction in a battery design, which half-reaction happens on the cathode
and which on the anode?
3. When chlorine gas is pumped through ammonium bromide aqueous solution:
a. Write the proper presentation of this chemical change.
b. Identify whether this reaction is a redox reaction.
c. Identify the oxidizing and reducing agents.
d. Used the standard reduction potential for half-cells to justify your answer.
4
e. To utilize this reaction in a battery design, which half-reaction happens on the cathode
and which on the anode?
4. Use the standard reduction potentials provided in the table on page 2 to predict whether the