Use standard reduction potentials to calculate the standard...

Use standard reduction potentials to calculate the standard free energy change in kJ for the reaction: 1) Pb2+(aq) + 2I-(aq) → Pb(s) + I2(s) Answer: kJ K for this reaction would be _________greater/less than one. Use standard reduction potentials to calculate the standard free energy change in kJ for the reaction: 2) Cd2+(aq) + 2Fe2+(aq) → Cd(s) + 2Fe3+(aq) Answer: kJ K for this reaction would be _________greater/less than one.

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Transcript

00:01 To calculate the standard free energy change, we first need to calculate the standard cell potential.

00:07 The reaction is pb2 +, reacting with 2i - to go to pb solid plus i2 solid.

00:21 So, to answer this question, we need to look up the standard reduction potentials for the two half reactions that when combined give us this overall reaction.

00:30 The cell standard will then be equal to the reduction potential for what is actually reduced.

00:41 We see that lead 2 plus is being reduced to lead solid.

00:46 And, according to the table i have, the reduction potential for pb2 plus going to pb solid is negative 0 .13 volts.

00:57 We then subtract from that what's happening at the anode where oxidation of iodide is occurring to iodine.

01:08 Because oxidation is occurring now instead of reduction, then we subtract off the reduction potential because the reaction is going in reverse.

01:16 So, it will be minus 0 .54 volts.

01:26 And, this gives us negative 6 .7, whoops, negative 0 .67 volts.

01:36 Delta g standard then is equal to negative nfe standard.

01:44 N is the moles of electrons transferred, which is 2 in this case.

01:48 Two electrons need to be acquired by lead 2 plus to become lead.

01:52 F is faraday's constant, 96 ,485.

01:58 And then, e standard we just determined to be negative 0 .67 volts...

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