Lesson 3: Spontaneity of Redox Reactions UNIT 7: Lesson 3: Spontaneity of Redox Reactions

Table of Standard Reduction Potentials Each half-reaction can go backward or forward, and is thus written using . When a half-reaction is part of a redox reaction, it goes in one direction only and is written using →. As written on the table, the forward reactions are reductions, and the backward reactions are oxidations.

Reactions in an Electrochemical Cell Suppose you have two half-cells. One contains Zn(s) and Zn2+(aq). The other contains Cu(s) and Cu2+(aq). The possible half-reactions are: Cu2+ + 2 e- Cu and Zn2+ + 2 e- Zn Cu2+ has a higher tendency to reduce than Zn2+, so the actual reactions that occur are: Cu2+ + 2 e- → Cu and Zn → Zn2+ + 2 e-

The Spontaneous Reaction Dance A reaction will be spontaneous if and only if there is a reactant to be reduced (on the left side) which is above a reactant to be oxidized (on the right side). Remember the dance: No, no, yes, no!

Brain Break! Spot It!

Important Notes Sometimes a chemical species appears more than once on the chart. Be sure to use the strongest oxidizing and reducing agents available! All species in the reaction must be present in order for it to occur!

Try This: Predict whether or not a spontaneous reaction will occur when: Cl2 is mixed with Ag Sn is mixed with Mn Ni2+ is mixed with Pb Write the equation for each spontaneous reaction above. 20 min

Homework: Pg. 199 #8 (a, c, e, etc.) and 14 5 min