berkeley review thermochemistry error??

[deleted380953]

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Does anyone know if theres an error on example 13 in the berkeley review thermochemistry chapter?

It seems to me that they added the delta H of H2O liquid instead of H2O gas, so in the solution it says:

6(-393.5) + 6(-286)


rather than: 6(-393.5) + 6(-242)


am I right or wrong?

 

[PingPongPro]

Its possible that the phase of H2O in the equation is incorrectly labeled as gas. If you look at 12 and 14, the H2O formed from combustion is in liquid phase. However, I think the combustion of glucose in our bodies does produce H2O in the gaseous phase, so you are probably right, that the book is wrong.

Its also quite possible that this error is fixed in the newest version of the book, but I'm not sure.

Its also incredibly funny how the book talks about the importance of paying attention to the phase for water in the very next example.

 

[deleted380953]

Its also incredibly funny how the book talks about the importance of paying attention to the phase for water in the very next example.

Ha, I noticed that too

must have been a bit awkward to the writers when they saw that

 

[BerkReviewTeach]

Ha, I noticed that too

must have been a bit awkward to the writers when they saw that

LOL!!! You have absolutely no idea how much you made my day. I help edit books from time to time, and I've gotten the speech from the chemistry author about things exactly like that.

 

[deleted380953]

LOL!!! You have absolutely no idea how much you made my day. I help edit books from time to time, and I've gotten the speech from the chemistry author about things exactly like that.

lol, I guess we're all human then

On a slight side note, I purchased my books in march, so does that really mean there's a new edition out already?

 

[sejin8642]

There is another error too. At the end of the thermochemistry chapter, the sub-section title "Carnot Cycle" should be changed to "Thermodynamic Cycle" because Carnot cycle refers to one specific thermodynamic cycle where isothermal and isentropic processes are involved. For example, If you look at the phase diagram in the section where one cycle is completed through which the phase changes between gas and liquid, you can see that it's not Carnot cycle. This is not one measly error that should be considered lightly (it gives false ideas on the entire section). This confused me for a while but I figured it out later.

 

[deleted380953]

There is another error too. At the end of the thermochemistry chapter, the title "Carnot Cycle" should be changed to "Thermodynamic Cycle" because Carnot cycle refers to one specific thermodynamic cycle where isothermal and isentropic processes are involved. If you look at the phase diagram in the book where one cycle is completed through which the phase changes between gas and liquid, you can see that it's not Carnot cycle. This is not one measly error that should be considered lightly (it gives false ideas on the entire section). This confused me for a while but I figured it out later.

if thats true, then it's textbook/khan academy time for me on this topic

 

[sejin8642]

if thats true, then it's textbook/khan academy time for me on this topic

Wikipedia is a good source on this topic if you know Calculus.

 

[BerkReviewTeach]

...the sub-section title "Carnot Cycle" should be changed to "Thermodynamic Cycle" because Carnot cycle refers to one specific thermodynamic cycle where isothermal and isentropic processes are involved...

This is not one measly error that should be considered lightly (it gives false ideas on the entire section). This confused me for a while but I figured it out later.

Wikipedia is a good source on this topic if you know Calculus.

I mean this as politely as possible, but stop for a moment and realize that you are taking the MCAT and not applying for physical chemistry graduate school. The P chem is watered down. There is no calculus on the MCAT. This does not mean that a basic idea of what an integral and derivative are won't help with some graph concepts, but too much knowledge can be a distraction at some point. Same thing goes for the Carnot cycle. As stated in the BR books, many examples have been brought down to the MCAT level (this goes for several experiments and machines). This is done so that the basic ideas are taught and not excessive details and overly complex math. If you can differentiate between the special case scenario for the Carnot cycle and understand the calculus, that is great for school but not necessary for the MCAT. Preparation involves learning the level of the exam as well as the material on the exam. I'm not saying you're not right in what you are saying; I'm saying that the BR books likely ignored that for whatever reason. Perhaps the MCAT writers have a history of using a general (non-exact) presentation of the Carnot engine. Who knows?

 

[Silverfalcon]

I mean this as politely as possible, but stop for a moment and realize that you are taking the MCAT and not applying for physical chemistry graduate school. The P chem is watered down. There is no calculus on the MCAT. This does not mean that a basic idea of what an integral and derivative are won't help with some graph concepts, but too much knowledge can be a distraction at some point. Same thing goes for the Carnot cycle. As stated in the BR books, many examples have been brought down to the MCAT level (this goes for several experiments and machines). This is done so that the basic ideas are taught and not excessive details and math. If you can differentiate between the special case scenario for the Carnot cycle and understand the calculus, that is great for school but not necessary for the MCAT. Preparation involves learning the level of the exam as well as the material on the exam. I'm not saying you're not right in what you are saying; I'm saying that the BR books likely ignored that for whatever reason. Perhaps the MCAT writers have a history of using a general (non-exact) presentation of the Carnot engine. Who knows?

Excluding calculus part (since MCAT doesn't test calculus), I find this comment ironic here... Of all sections in BR books, Thermodynamics chapter with last part about Carnot cycle, refrigerator, heat pumps, etc... is one of the most "excessive details and math" part I've read in those books. And of course, after 4 pages of reading, the authors finally say, "Well you don't need to know all these..." Nice, right?

 

[sejin8642]

I mean this as politely as possible, but stop for a moment and realize that you are taking the MCAT and not applying for physical chemistry graduate school. The P chem is watered down. There is no calculus on the MCAT. This does not mean that a basic idea of what an integral and derivative are won't help with some graph concepts, but too much knowledge can be a distraction at some point. Same thing goes for the Carnot cycle. As stated in the BR books, many examples have been brought down to the MCAT level (this goes for several experiments and machines). This is done so that the basic ideas are taught and not excessive details and overly complex math. If you can differentiate between the special case scenario for the Carnot cycle and understand the calculus, that is great for school but not necessary for the MCAT. Preparation involves learning the level of the exam as well as the material on the exam. I'm not saying you're not right in what you are saying; I'm saying that the BR books likely ignored that for whatever reason. Perhaps the MCAT writers have a history of using a general (non-exact) presentation of the Carnot engine. Who knows?

I totally agree with you in terms of how much we are expected to know and what to discard. But at the same time, precise knowledge on the MCAT must be obtained. Since many examples in the "Carnot cycle" section of the BR book are non-Carnot cycle diagrams, some of the equations that work on Carnot cycle do not work on other cycles. For example, the efficiency equation, which is e = 1-Tc/Th, does not work on other thermodynamic cycles (the gas-liquid phase diagram in the book is, I believe, Brayton cycle). There are many MCAT examinees who are familiar with advanced Thermodynamics (Physics majors such as myself or Mechanical engineering majors) and they, many times, rely on the outside knowledge that they obtained through undergraduate work to better understand MCAT materials, especially PS. It usually leads to higher score. If, for the sake of general studiers, the materials are too simplified to the point where wrong information must prevail, it brings confusion to those who wish to solidify what they already know. And in the thermodynamic cycle section of BR, the author, I believed, failed to deliver that precision (Don't get me wrong, I love BR books. They're excellent source of passages that you cannot find anywhere else except AAMC FLs).

 

[deleted380953]

Excluding calculus part (since MCAT doesn't test calculus), I find this comment ironic here... Of all sections in BR books, Thermodynamics chapter with last part about Carnot cycle, refrigerator, heat pumps, etc... is one of the most "excessive details and math" part I've read in those books. And of course, after 4 pages of reading, the authors finally say, "Well you don't need to know all these..." Nice, right?

well the author also says "As of 2000, the heat engine has yet to appear on the new version of the mcat"

11 years seems like a big gap and you never know......

 

[Hershi]

In the same chapter, the q= mCdelta T examples ... did anyone notice how the Temperature is in Celcius but the examples arent converting to Kelvin? For example 8.16, its 37 C in the example they simply put 37k, shouldnt it be 37
+273?

 

[BerkReviewTeach]

In the same chapter, the q= mCdelta T examples ... did anyone notice how the Temperature is in Celcius but the examples arent converting to Kelvin? For example 8.16, its 37 C in the example they simply put 37k, shouldnt it be 37
+273?

deltaT is the same value whether it's in degrees Celcius or kelvins. I assume the conversion between units is omitted because it's an unnecessary extra step that consumes time.

 

[riddler]

I've not taken an advanced thermodynamics/thermochemistry course and so I have only a very basic understanding of these cycles.

Would wikipedia be enough to clarify my understanding enough of the difference between Carnot Cycle vs other cycles? I don't want to have an entirely wrong idea of what the Carnot Cycle is after reading the 4 pages in BR.