Spontaneity. Half Reactions Determine the half reactions and net equation for the reaction between silver chloride and solid copper.

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Presentation transcript:

Spontaneity

Half Reactions Determine the half reactions and net equation for the reaction between silver chloride and solid copper

Spontaneous Reactions Spontaneous reaction will occur with no input of energy!

Experimental Evidence place 2 substances in contact and see if they react. if a reaction occurs, 1 substance is oxidized (loses electrons) and 1 is reduced (gains electrons)

Stronger oxidizing agent (gets reduced) has greater affinity for electrons (more electronegative)

So What?! Spontaneous redox reactions are used in batteries as well a biochemical reactions like cellular respiration!

SOA above SRA for a reaction to be spontaneous, the oxidizing agent must be higher on the chart than the reducing agent think it requires no energy to roll downhill!

Example 1 4 unknown susbtances are being analyzed in oxidation- reduction studies. Each substance has a form that acts as an oxidizing agent (cations usually) and a reducing agent (solid metals usually). All reactions involve only 1 electron. The following table was constructed with a * indicating a reaction was observed. A(s)B(s)C(s)D(s) A+(aq) B+(aq)*** C+(aq)* D+(aq)**

The oxidizing agent with the most reactions is the strongest oxidizing agent, and the strength goes down from there!

Example 2 In a children’s chemistry set, a common experiment involves placing iron shavings in a solution of copper(II)sulfate. Predict whether or not this reaction would be spontaneous!

Redox Tables By testing the reactions of different oxidizing (and reducing) agents a redox table can be constructed. See p.9 in blue booklet

Strongest oxidizing agent at the top (gets reduced [gains electrons] easiest) Strongest reducing agent at the bottom (loses electrons easiest) Label it on your table