Understanding Hess's Law: An Inquiry

[vjk2]

So in Hess's law, I have a question on the why.

from an example in my book,

c+h20-> co+h2

and the intermediary reactions are

C+o2 ->Co2
2CO+O2->2Co2
2H2+O2->2h2O

Along the way, the second reaction is reversed and halved.

Now, Hess's law says that the pathway is irrelevant. But, in the actual physical reaction in the original, I do not believe that these intermediary steps actually take place. Especially the reversing of the second, since the single arrow pointed right would indicate that it is exceedingly difficult to separate the product into its component reactants.

I think that it may have something to do with innate ratios of energy between certain compounds, but I'm not sure.

Any thoughts?

Thanks

 

[Navin A S]

for your question! Hess's Law is based on the fact that energy is conserved in a chemical reaction. The reaction pathways don't necessarily reflect the actual physical reaction in the original, but it does allow us to calculate the energy changes that would occur in the reaction. In other words, the energy changes are independent of the pathway taken and only depend on the reactants and products involved. So, even though the second reaction is reversed and halved, the overall energy change will be the same as if it were done directly in one step.

 

[quicknote]

for your inquiry about Hess's Law. Let me start by explaining the concept behind Hess's Law. It is a fundamental principle in thermodynamics that states the enthalpy change for a reaction is independent of the pathway taken to reach the final products. In other words, the total enthalpy change of a reaction is the same regardless of whether it occurs in one step or multiple steps.

Now, let's address your specific question about the intermediary reactions in the example you provided. The reason for these intermediary steps is to show the conservation of energy in the overall reaction. In the first reaction, carbon (C) reacts with oxygen (O2) to form carbon dioxide (CO2) with a certain amount of energy released. In the second reaction, carbon monoxide (CO) reacts with oxygen to form carbon dioxide with a different amount of energy released. By combining these two reactions, we can see that the oxygen and energy released in the first reaction is exactly what is needed for the second reaction to occur. This is known as energy conservation and is a key principle in Hess's Law.

In regards to your concern about the second reaction being reversed and halved, this is simply a mathematical manipulation to ensure that the overall reaction is balanced. It does not necessarily mean that these intermediary steps are physically occurring in the reaction. As you mentioned, the single arrow in the original reaction indicates that it is a spontaneous reaction and does not require additional energy to separate the products. This is also consistent with the concept of energy conservation in Hess's Law.

Overall, the use of intermediary reactions in Hess's Law is simply a tool to show the conservation of energy and to ensure that the overall reaction is balanced. It does not necessarily represent the physical pathway of the reaction. I hope this helps clarify your understanding of Hess's Law. If you have any further questions, please don't hesitate to ask.