Many oxides of nitrogen have positive values for the...

Key Concepts

Standard Free Energy of Formation

This concept refers to the Gibbs free energy change that accompanies the formation of one mole of a compound from its elements in their standard states. A positive value indicates that the formation process is non-spontaneous under standard conditions, meaning that the compound is thermodynamically less stable relative to its constituent elements.

Reaction Enthalpy and Bond Energies

In forming a compound such as NO, energy must be invested to break the strong bonds present in the diatomic molecules (like the triple bond in N? and the double bond in O?). The energy released upon forming new bonds in NO may not be sufficient to compensate for the energy required to break these very stable bonds, resulting in an overall endothermic reaction that contributes to a positive free energy of formation.

Electronic Structure and Radical Nature

NO is a radical with an unpaired electron, which affects its stability and reactivity. Its electronic configuration leads to unique bonding characteristics that do not fully stabilize the molecule compared to the starting materials, further explaining why the free energy of formation remains positive despite the presence of chemical bonds.

Transcript

00:01 Hello, today we're going to be discussing why many of the oxides of nitrogen have positive values for the standard free energy formation and formation.

00:15 And that's going to be using no as an example.

00:18 So why is this the case? okay, so we, in the problem, we're given that we're supposed to explain why the standard free.

00:31 Energy formation it has positive values for nitrogen oxides so immediately i would write down the gibbs free energy formula which goes something like this delta g gives free energy equals delta h minus t temperature delta s and this is uh this is let me write this in entropy for heat red for heat and entropy is delta s entropy so change in entropy before and after the reaction and changing entropy before and after reaction and we have nitrogen over here nitrogen and this horrible we have nitrogen nitrogen atom and that's usually as n2 that's the before it reacts with oxygen it's gaseous nitrogen and after it's going to turn into some n oxide and that's going to be also gaseous and that's going to be the after and i'm not writing a formula because there should be a i'm just writing a conversion from n2 to no, no chemical formulas here.

02:31 But this is sufficient, this writing this and writing the conversion is sufficient to figure out why delta g is positive, why is delta g positive for nitrogen oxides.

02:54 And there's a reason for that.

02:56 If we look at a bond energy chart, we can see that.

03:00 That the nn bond, this bond over here, this is the nn and then bond.

03:11 It has a energy of bond entropy rather.

03:18 It's essentially the energy of the bond, how strong the bond is.

03:22 It is 163 kilojoules per mole.

03:34 And the no energies, bond energy that's going to be much higher 201 and we're considering no as an example but there are other oxides such as nf nbr and nitrogen bromine it's 201 kilojoules my bed 2 1 kilojoules per mole 2 1 kilojoules per mole and without me explaining it you can see that the this is the before before and the after and as i said without explain without without that without explaining it you can see that clearly this is a smaller number than 201 okay my bad it's not drawing here all right so you see the number 201 and you see 163 and why that is we can just make some space since you understand this.

05:15 The bond energy just gives it away...

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