graphing le chateliers (1 Viewer)

[sssona09]

so if we have the equation of ammonia synthesis:
N2 + 3H2--> 2NH3

and the volume of the reaction vessel is halved 10 seconds after the reactants are first mixed. Skeych a graph of Nitrogen and Hydrogen concentration vs time Start the graph at the time when the reactants are first added and assume equilibrium was reached before the 10 second mark.

how would it roughly look? thank you

 

[captainhelium]

When changing the volume of the reaction vessel, you'll have to compare each side of the equilibrium in terms of how much gaseous moles are produced.

In the Haber Process (i.e. ammonia synthesis), we have 4 gaseous moles on the left hand side in total and 2 gaseous moles on the right hand side in total.

When halving the volume of the reaction vessel, the pressure inside the reaction vessel increases. This means that according to Le Chatelier's principle, the equilibrium will try to decrease the pressure and hence it will shift towards the right (as it has less gaseous moles and hence lower pressure), producing a greater concentration of ammonia. This also means that the concentration of nitrogen and hydrogen gas will decrease.

Also, in terms of the shape of the graph, it actually isn't just a smooth decrease in N₂ and H₂ concentration and a smooth increase in NH₃ after the 10 second point. What actually happens initially is that at the 10 second mark all the substances have a sudden vertical-spike increase in concentration - this is because when you halve the volume, essentially the concentration of everything shoots up momentarily (since a smaller space with the same number of substances results in higher concentration of everything). It is only after this spike that the gradual decrease in N₂ and H₂ occurs and the gradual increase in NH₃ happens.

I can't seem to find a picture of it online but I hope that explanation helped. If you need any further explanation let me know and I'll do my best to assist!

Edit: I also forgot to mention that at 0 seconds, you are inputting the reactants into the reaction vessel. This means that the concentration of N₂ and H₂ initially is high but then gradually decreases as it creates NH₃ as the system tries to reach equilibrium. Then the concentration of the reactants and products are in equilibrium before the change in pressure happens at the 10 second mark. ichila101's graph is a good picture of what happens.

 

[ichila101]

Essentially a rough sketch of what captainhelium explained, though I do not advise using paint for sketching .

 

[sssona09]

Thank you both!!! <3