Le Chatelier

[adrakdavra]

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It is possible to convert graphite into diamond via various chemical processes. Based on the information in the passage, which of the following would facilitate increased amounts of diamond assuming that the system is in equilibrium?

A.Higher pressures
B. Lower temperatures
C. A catalyst
D. None of the above
INCORRECT:
Your Answer: D
Correct Answer: A but why???😎

 

[diarrhea joe]

To go from graphite to diamond you need to put energy in to push the reaction in a certain direction.
Graphite + Energy (Your option here is pressure) ---> Diamond
The only option that does that is higher pressure. More pressure --> more diamond.

According to lechatelier, more stuff on the left pushes the reaction to the right (you get more product). If you add something on the left like pressure, you're gonna get more stuff on the right.

If system wasn't in equilibrium (having a ****load of graphite) catalyst might work, but at equilibrium the reaction is pretty much going nowhere so catalyst won't do jack.

 

[adrakdavra]

To go from graphite to diamond you need to put energy in to push the reaction in a certain direction.
Graphite + Energy (Your option here is pressure) ---> Diamond
The only option that does that is higher pressure. More pressure --> more diamond.

According to lechatelier, more stuff on the left pushes the reaction to the right (you get more product). If you add something on the left like pressure, you're gonna get more stuff on the right.

If system wasn't in equilibrium (having a ****load of graphite) catalyst might work, but at equilibrium the reaction is pretty much going nowhere so catalyst won't do jack.

How do you know that pressure is added to the left side and not the right side. I know with gases we can look at the moles and know which size has a higher pressure.

should we always assume that adding pressure mean the direction toward the lower moles side? and why ???

The more I think about it, I realized that pressure increases the whole system (reactants + products) , then the side that has higher moles will move the opposite direction to alleviate the pressure in that side to bring the rxn back to equilibrium.
However, the passage wasn't that clear about which side has higher moles.
They provide us with the density of both, and indicating that diamonds has a higher density, so I am guessing the higher density will mean higher mass and lower volume and higher pressure, but if that is the case shouldn't the Rxn direction go back toward graphite ???

 

[adrakdavra]

Or may be solids are diff then gases. therefore , higher pressure favor lower volume, which in this case it will go toward diamonds because of its lower volume.

any comments ....

 

[ema2iur]

Is this question strictly limited to Le Chatelier concept's or can you factor in phase diagrams? When looking at phase diagrams, solids are favoured over other phases at higher pressures and lower temperatures. Further, if a substance is an allotrope like carbon with different forms such as graphite and diamond, which are both solids, then the more dense substance (diamond) will be favoured at higher pressures. When looking at changes in pressure/volume from a Le Chatelier perspective, don't substances have to be in gaseous form for Le Chatelier to even be considered (Which they aren't in this case so it shouldn't be considered). However, phase diagrams could apply...