TBR General Chemistry Section III Equilibrium, Example 3.14

[PBody500]

If the following reaction represents a system at equilibrium, indicate which statement is NOT true.

PCl3(g) + Cl2(g) <------> PCl5(g)

A) Increasing the pressure would cause a decrease in PCl3
B) Adding PCl5 would cause an increase in PCl3
C) Increasing the volume would cause an increase in PCl3
D) Removing Cl2 would cause a decrease in PCl3

So I personally had no idea of the answer b/c I thought multiple answers were not true. I thought this because on the previous page, TBR explains that Increased pressure = shifts left, which = increase PCl3(g). Hence I thought A was false and the correct answer.

I understand B fine. For C, they increased the Volume. As stated on the previous page, Increase in Volume = shift right. This would mean PCl3 would decrease so I thought this was also False and could be the answer.

For D, removing Cl2 (reactant) would = Increase in reactant to compensate, thus Increase in PCl3. So now I thought D was also correct b/c its false.

I think I found my problem though. The previous reaction used as an example was N2O4(g) <---> 2NO2(g).

Since that reaction is not in equilibrium does that change how pressure, volume, etc will effect the reaction? B/c if so then I understand the reasoning. I just want to make sure I'm on the right track here.

First post sorry so long. Thank you and good luck to all studying!

---

Members don't see this ad.

 

[aldol16]

Since that reaction is not in equilibrium does that change how pressure, volume, etc will effect the reaction? B/c if so then I understand the reasoning. I just want to make sure I'm on the right track here.

Two completely different reactions that are both at equilibrium. The key difference you missed is that in the one you list here, you have two moles of gas on the left and one mole of gas on the right. In the other one, there is one mole of gas on the left and two moles of gas on the right. That's the key difference because say you increase the pressure on a system. It's going to want to shift to reduce that added pressure. How does it do that? Well, it'll shift to the side that results in fewer moles of gas. So for the phosphorus system here, it's going to shift right to reduce the number of moles of gas (2 moles of gas react to give 1 mole of gas). For the other system, it'll shift left because there are two moles of gas on the right and only one on the left.

 

[PBody500]

Two completely different reactions that are both at equilibrium. The key difference you missed is that in the one you list here, you have two moles of gas on the left and one mole of gas on the right. In the other one, there is one mole of gas on the left and two moles of gas on the right. That's the key difference because say you increase the pressure on a system. It's going to want to shift to reduce that added pressure. How does it do that? Well, it'll shift to the side that results in fewer moles of gas. So for the phosphorus system here, it's going to shift right to reduce the number of moles of gas (2 moles of gas react to give 1 mole of gas). For the other system, it'll shift left because there are two moles of gas on the right and only one on the left.

Got it! I was getting caught up in directions and not the actual makeup of the reaction.

Thank you!

 

[Pono_0001]

ya don't memorize direction but think about moles of gas instead