AP Chemistry Help?

Question

How will the equilibrium position of a gas-phase reaction be affected by changing the volume of the reaction vessel?

( i think the greater the volume, the less the concentration would be therefore the less the equilibrium position would be)

Are there reactions that will not have their equilibria shifted by a change in volume?
yes or no
Explain.

(I don't really know here so if you could explain it to me that'd be great)

Answer 1

Suppose you look at two different gas phase reactions:

N2 + 3 H2 --> 2 NH3
and
H2 + Cl2 --> 2 HCl

In the first one you have 4 moles of gas on the left and only two on the right. In the second one, you have 2 moles of gas on both sides.

So, if you have the first reaction sitting at equilibrium and you increase the volume of the container, the equilibrium will shift toward the side with more moles of gas. If you decrease the volume, the equilibrium will shift toward the side with fewer moles of gas. The same result will occur if you change the pressure in the container.

In the case of the second reaction, since both sides of the equilibrium have the same number of moles of gas (2 on each side), this equilibrium WILL NOT be affected by changing the volume or the pressure.

Hope that helps.