GS-1 Physical Sciences Question 12

[kkalita5051]

I just have a quick question. Why doesn't the partial pressure of oxygen increase as well? Thank you!

[mcat_premed3832]

In order for the partial pressure of oxygen to increase, that would mean that the reaction had shifted towards the left. For that to happen, the strain on the system must be coming from the right which means either: (1) the temperature increases leading to more oxygen and SO2 production; (2) SO3 was added to the equilibrium thus a left shift would relieve that strain; (3) a reduction in pressure which favors the left side which has 3 moles as opposed to the right side that has just 2 moles.

None of the above happened in this problem. In summary, oxygen can't increase because of Le Chatelier's Principle.

[IrvPhill6636]

I'm a bit confused. I understand why SO3 would go up, but doesn't the question ask what the partial pressure will be when it reaches equilibrium again?

Or does that not matter because the first equilibrium expression was for a specific temperature and because we have a new temperature the equilibrium will always be different at the new, lower temperature?

[admin]

I'm a bit confused. I understand why SO3 would go up(CORRECT), but doesn't the question ask what the partial pressure will be when it reaches equilibrium again (NOT REQUIRED TO DO THE CALCULATION BUT ONLY THE CONCEPTUAL ASPECT IS ASKED AS PER THE CORRECT ANSWER GIVEN ABOVE IT IS A STRESS ADDED TO THE SYSTEM BY LE CHATELIER’S)?

Or does that not matter because the first equilibrium expression was for a specific temperature and because we have a new temperature the equilibrium will always be different at the new, lower temperature?SEE BELOW:

To answer your question, the first equilibrium is temperature specific and so as such, at a lower temperature, a new equilibrium is established and thus, it does not matter and the answer is that SO3 partial pressure will increase due to the temperature change effect on the thermodynamic properties and due to the stress on the system as per Le Chatelier’s Principle.