Question about increasing P and LeChatlier's

[pitt1166]

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This question has me confused.

We are given CO2(g)+ C(s) -> 2CO(g), and told that it is taking place in a sealed furnace.

Question asks...

When the system is stabilized at 1200K, a sample of Helium was injected. What should happen to the amount of CO2 gas in the system?

The answer Kaplan gives is that Helium is unreactive (obviously), and while adding it does increase the total pressure, it doesn't affect the partial pressure of the reacting gases (Dalton's Law), so they keep behaving as if Helium was not present.

But I figured that increasing total P would favor the side with fewer moles of gas, per LeChatlier. Am I incorrect, does that only come in to play with partial pressures?

Manythanks.

 

[rocuronium]

Trying thinking about it in terms of concentrations.

If you increase the pressure inside the container without increasing the volume of the container (e.g. adding an inert gas) you are not changing the concentrations of reactants or products. Therefore, there is no shift in the equilibrium.

If, however, you increase the pressure while allowing the volume to change, you would be changing the concentrations of the products and reactants. This would lead to the shift in equilibrium either right or left, depending on the number of moles of gas on either side.

I hope that helps.

 

[engineeredout]

If you were to add more CO2 to the system, the system would attempt to compensate for the increased CO2 by using more of it up, IE producing more CO; therefore the equilibrium would be shifted to the right side.

Anything added to the system that is not part of the reaction, just ignore. It won't have an effect on equilibrium.