NH4+ br test

[2010premed]

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How do you know that the molecule in NH4+ repel each other?

 

[loveoforganic]

If you're asking why ammonium ions repel one another, it's because like charges repel.

 

[2010premed]

Huh, well the original question was which of the following has a negative a term (from Preal + a n^2/V^2
I was thinking that iw was asking about the N and H, but I'm not sure anymore...
does the a value refer to the bonds between N and H or NH4+ and other NH4+?

 

[BerkReviewTeach]

Huh, well the original question was which of the following has a negative a term (from Preal + a n^2/V^2
I was thinking that iw was asking about the N and H, but I'm not sure anymore...
does the a value refer to the bonds between N and H or NH4+ and other NH4+?

You need to look at the entire question and apply POE. Molecules that attract one another have a (+) a value, because you need to correct for the reduced pressure (relative to ideal pressure) associated with attraction. For the a term to be (-), the particle must be repelling one another.

Like charges repel. NH4+ molecules are cations, so they will repel one another and in essence explode from the middle of the container and hit the walls more often. This raises the pressure (relative to ideal pressure), so the (-) a term helps lower the calculated pressure value and make it equal to ideal pressure (which is all the van der Waals equation is really doing).