TBR Chapter 6 Question 4 Chemistry

This forum made possible through the generous support of SDN members, donors, and sponsors. Thank you.

StretchDoe

Full Member
7+ Year Member
Joined
Feb 28, 2016
Messages
79
Reaction score
5
The question states How does the molar volume of ammonia gas compare to that of an ideal gas?

The answer is the molar volume of ammonia gas is less than that of an ideal gas because of attractive forces.

I partially understand this, however I thought ideal gases do not have any volume so wouldn't ammonia gas have a larger volume than an ideal gas?

Members don't see this ad.
 
The question states How does the molar volume of ammonia gas compare to that of an ideal gas?

The answer is the molar volume of ammonia gas is less than that of an ideal gas because of attractive forces.

I partially understand this, however I thought ideal gases do not have any volume so wouldn't ammonia gas have a larger volume than an ideal gas?
Real gases deviate from ideal gases in both directions. Their stickiness means a mole takes up LESS space than expected. Their non-zero molecular volume means A mole takes up MORE space than expected.

This question is testing whether you can reason which effect is stronger.

NH3 molecules are pretty small. The volume effect is going to be pretty small.

NH3 can do hydrogen bonding. The stickiness factor is gonna be huge.

Stickiness wins. A mole of NH3 is going to take up less volume than that predicted by the ideal gas law.

Good question!
 
  • Like
Reactions: 1 user
There are actually TWO Question #4s in Chapter 6. Are you talking about Question #4 from the 25 Review Set or Question #4 from Phase II?

In Question #4 of the 25-Question set, you should take it at face value that after reaching equilibrium the two solutions will have equal concentrations. That value will be somewhere between the two starting molarities of 0.50 M and 0.70 M, which means it must be greater than 0.50 M.

In Question #4 of Phase II, you should take note that they are asking about the remaining solution in the flask after initial vapor leaves the distilling flask. The initial vapor will be richest in methanol, because it has a lower molecular mass than ethanol (and thus a lower b.p.). Over time, the solution will become richer in ethanol, although both ethanol and methanol moles will be decreasing. If this is your question, what part is not clicking?

Both of these passages are based on experiments, which is key on the MCAT now. It is important to have a good understanding of experimental design and reasoning, which is why the book now has so many of those types of passages. If you have questions on any other experiment passages, post them.
 
There are actually TWO Question #4s in Chapter 6. Are you talking about Question #4 from the 25 Review Set or Question #4 from Phase II?

In Question #4 of the 25-Question set, you should take it at face value that after reaching equilibrium the two solutions will have equal concentrations. That value will be somewhere between the two starting molarities of 0.50 M and 0.70 M, which means it must be greater than 0.50 M.

In Question #4 of Phase II, you should take note that they are asking about the remaining solution in the flask after initial vapor leaves the distilling flask. The initial vapor will be richest in methanol, because it has a lower molecular mass than ethanol (and thus a lower b.p.). Over time, the solution will become richer in ethanol, although both ethanol and methanol moles will be decreasing. If this is your question, what part is not clicking?

Both of these passages are based on experiments, which is key on the MCAT now. It is important to have a good understanding of experimental design and reasoning, which is why the book now has so many of those types of passages. If you have questions on any other experiment passages, post them.

Unfortunately, I only have the older editions of TBR. Therefore, it's the older chemistry book, chapter 6 gases and gas laws, question 4, part of the 100 questions to end the chapter.
 
Top