9.3 REACTIVITY (Predicting Spontaneity of Redox Reactions)
*If one particle is able to pull electrons away from another particle, a _________________redox reaction will occur. (i.e. one that does
not require a continuous input of energy in order to continue.)
Ex. 1: Overall Equation:
Zn(s) + CuSO4(aq)  ZnSO4(aq) + Cu(s)
Net equation:
Ex. 2: Overall Equation:
RA = _______; OA =________
Cu(s) + 2AgNO3(aq)  Cu(NO3)2(aq) + 2Ag(s)
Net Equation:
RA = _______; OA =________
*Both examples 1 & 2 reactions occur__________________________.
*However…
Ex. 3: Overall Equation:
Cu(s) + Ni(NO3)2(aq)  NO REACTION
*Reaction does not occur spontaneously…why?
*Electron transfers can be thought of as a “competition” for electrons. (“Tug-of-War”) *In example 1, the oxidizing agent, ______, is
able to pull electrons away from _____ atoms. (i.e. Cu2+ ions have a stronger attraction for Zn’s valence electrons than Zn does.)or …
Cu2+ ions are able to __________ Zn atoms.
Therefore:
Zn(s) + Cu2+(aq)  spontaneous
Cu(s) + Zn2+(aq)  nonspontaneous (Zn2+ ions are not able to oxidize Cu atoms)
*In ex.2, Ag+ ions are able to oxidize Cu atoms. (i.e. reaction is _________________)
*In ex.3, Ni2+ ions are unable to oxidize Cu atoms. (i.e. reaction is __________________)
*Is there a way to determine whether a redox reaction will occur spontaneously or not?...without doing an experiment.
*We can rank metal ions (usually_____________ agents) according to their ability to react with solid metals (____________ agents).
THOUGHT-LAB:
Consider a series of experiments aimed at determining the reactivity of the following metals: Ag, Cu, Pb, and Zn.
EXPERIMENT ONE: Each metal is placed in one of four beakers. Each beaker contains Ag+(aq).
EXPERIMENT TWO: Each metal is placed in one of four beakers. Each beaker contains Cu2+(aq) . (…and so on)
Summary of results:
Solution Containing
Reacted with
Ag+
Cu2+
Pb2+
Zn2+
# of Reactions
Reactivity Order
Most ------------------------------------------------------------------- least
*Which of the four oxidizing agents in this example is the strongest?  _____ ; weakest? _____
*Recall: Strong oxidizing agents are “good at” attracting electrons away from other metals; that is, they are readily reduced.
*What classes of substances (e.g. metals, nonmetals, acidic, basic) usually behave as
a) reducing agents? - __________________________
b) oxidizing agents? - _________________________
Constructing a table Relative Strengths of Oxidizing Agents and Reducing Agents
*The strongest oxidizing agent (SOA) is always located in the lower ______ corner of this type of table. The strongest reducing
agent (SRA) (i.e entities that give up electrons readily) is located in the upper _________part of the table.
*By convention, the half- reactions represented in this type of table are always written as ___________. *Double arrows are used to
indicate that the half-reaction can be read from left to right (reduction) or from right to left (oxidation). Therefore, the double arrows
do not represent chemical ______________ in this case. For previous THOUGHT-LAB the table would be:
THE SPONTANEITY RULE: A spontaneous reaction only occurs if the OA is ______________ the RA in a table of relative
strengths of oxidizing agents and reducing agents. (The table in your text and Data Booklet. More on this later….)
1. Practice: From the following evidence, construct a table of relative strengths of OAs and RAs. Label and circle the SOA and SRA.
a)
 eous

 Co2+(aq) + Pd(s)
Co(s) + Pd2+(aq) Spontan
 eous

 Pd2+(aq) + Pt(s)
Pd(s) + Pt2+(aq) Spontan
 eous

 Mg2+(aq) + Co(s)
Mg(s) + Co2+(aq) Spontan
b)
Cd(s) + 2H+(aq)
Hg(s) + 2H+(aq)
Be(s) + Cd2+(aq)
Be(s) + Ca2+(aq)
c)
Ag(s) + Br2(l)  AgBr(s)
Ag(s) + I2(s)  no evidence of reaction
Cu2+(aq) + I-(aq)  no evidence of reaction
Br2(l) + Cl-(aq)  no evidence of reaction
Spontan
 eous

 Cd2+(aq) + H2(g)
Nonspontan eous
    Hg2+(aq) + H2(g)
Spontan
 eous

 Be2+(aq) + Cd(s)
Nonspontan eous
    Be2+(aq) + Ca(s)
2. A student is required to store an aqueous solution of iron(III) nitrate. She has a choice of a copper, tin iron, or
silver container. Use the table of relative strengths of oxidizing and reducing agents in your Data Booklet to
predict which container would be most suitable for storing the solution. Explain your prediction.
More Practice (Nelson Text) p. 676 #1-3; p. 678 #10, 11, 13
THE REACTIVITY OF METALS “HIERARCHY”
(i.e. THE ACTIVITY SERIES OF METALS)
COMPLETE THE FOLLOWING:
1. a) Highlight “hydrogen” in the above list. Why is it in this list of metals?
Examples: Write balanced chemical equations (with state symbols) for the following.
i) lithium plus hydrochloric acid:
ii) zinc plus sulfuric acid:
iii) copper plus hydrochloric acid:
iv) silver plus nitric acid:
b) Locate and highlight the half reaction pertaining to acids (H+/H2) on the IB electrode potential table.
c) Locate all the metals in part a) (on the IB table) and compare their positions to the position of H +. How can their relative positions
be used to predict spontaneity?...whether a reaction will occur spontaneously or not.