Energy Transfers

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Re: Energy Transfers

Post by goodcheer »

SWAnG wrote:hmm but are you not transfering the electrical current into the electrolyte solution (chemical) then back into the circuit?

Seems like the ETS would be M-C-E. M being some mechanical way to dump the salt. C being the chemical solution created by the salt and water. E being the electrical current that begins to flow. But, would there be enough electrical current to do anything else, say, turn on a motor?
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Re: Energy Transfers

Post by SWAnG »

I'm saying directing electricity into the salt water solution should count as ECE right?
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Re: Energy Transfers

Post by wlmeng11 »

SWAnG wrote:I'm saying directing electricity into the salt water solution should count as ECE right?
I would say no because of Section 4 line 4-5 "A single Action or component must contribute to only one scoreable Transfer". While passing an electrical current through salt water does cause a chemical reaction (an electrolysis reaction that produces hydrogen and chlorine gases, so be careful), the initial electrical current is the same current as the output. It would be like using an electrical current to power a motor and taking the output to be somewhere farther along the same conducting loop and calling that E-M-E, rather than applying current to the coil of a relay to close a switch to send current through the output terminals, where the input and output electrical currents are distinct.
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Re: Energy Transfers

Post by chalker »

wlmeng11 wrote:
SWAnG wrote:I'm saying directing electricity into the salt water solution should count as ECE right?
I would say no because of Section 4 line 4-5 "A single Action or component must contribute to only one scoreable Transfer". While passing an electrical current through salt water does cause a chemical reaction (an electrolysis reaction that produces hydrogen and chlorine gases, so be careful), the initial electrical current is the same current as the output. It would be like using an electrical current to power a motor and taking the output to be somewhere farther along the same conducting loop and calling that E-M-E, rather than applying current to the coil of a relay to close a switch to send current through the output terminals, where the input and output electrical currents are distinct.
As usual, this isn't the place for official comments or clarifications.... how my opinion on this is:

We've been pretty clear in the rules and FAQs that we don't expect energy conversions (e.g. mechanical energy being converted to electrical via a generator), but rather chains of energy transfers (e.g. actions that rely upon a certain energy type).

I think everyone agrees that if you have a mechanical switch that closes to allow current to flow through a circuit and do something, you have a M->E energy transfer.

Taking this a step further, if the switch is made of nichrome (say from a manal thermostat;) and you heat it up which causes it to close to allow current to flow through a circuit and do something, I'd propose you have a T->E energy transfer. Some people might nitpick and say it's T->M->E, but I think the spirit of rule 4 about 1 action/component only contributing to a single transfer prevents that from being counted.

Following that same logic, if you change the conductivity of a solution (say by dumping salt into water) to allow current to flow through a circuit and do something, you have a C->E energy transfer. Again, some might nitpick and say that it's M->C->E because you first physically moved the salt into the water, however in this situation you can ignore the M part I think and just count the C->E.

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Re: Energy Transfers

Post by goodcheer »

SWAnG wrote:I'm saying directing electricity into the salt water solution should count as ECE right?

I agree with Chalker. The first E would not count because you don't have any electrical current flowing until you add the salt to form the chemical solution. So, C-E or M-C-E should work. Adding the salt would be like turning on a chemical switch to the electrical current. Also, the amount of chlorine gas produced will be minute unless you are doing it on a massive scale. You can get a little bang if you collect the hydrogen gas. Again, not enough for the Hindenburg, but do be careful.
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Re: Energy Transfers

Post by torqueburner »

goodcheer wrote:
I agree with Chalker. . .Adding the salt would be like turning on a chemical switch to the electrical current. . .
Sorry in advance, this is a bit long winded. . .

I would say that dissolving NaCl in water is a physical change, not a chemical change. I spoke to our current and past high school chemistry teachers, who both confirmed this. A quick on-line search finds many others who agree, including:

http://chemistry.about.com/od/matter/a/ ... Change.htm

http://en.wikipedia.org/wiki/Physical_change

http://www.inquiryinaction.org/chemistryreview/solids/


On the other hand, if you look hard enough, you can find a (very small) minority who say otherwise. This is the only dissenting opinion I found, though there may be more out there somewhere:

http://www.answers.com/Q/What_is_the_di ... issolution

This one states "When adding water: NaCl (s) => Na+ (aq) + Cl- (aq) This is a very soluble ionic compound and it changes from a neutral compound to ions, a chemical change."


In the end, it is the event supervisor who will decide whether conducting current through a saline solution qualifies as C-E. If that supervisor was me, I would not, as there is a preponderance of evidence that says otherwise. But just as I was able to find a dissenting opinion, you may find a Mission supervisor who would allow this. It never hurts to contact the supervisor and ask in advance.

I have supervised Mission numerous times, and would always ask to see device ETLs, TSL's, ASL's (the sequence list whatever it is called in a particular year) in advance. This gave me the opportunity to notify the students if there was something like the above that I would not accept. I would offer them the opportunity either to convince me otherwise (preponderance of evidence again), or to make changes to their device so that it would be consistent with my interpretation of the rules. It is a shame that the current rules do not allow for this.
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Re: Energy Transfers

Post by chalker »

goodcheer wrote: ......I would say that dissolving NaCl in water is a physical change, not a chemical change. I spoke to our current and past high school chemistry teachers, who both confirmed this. .....
As always, this is not the place for official comments or clarifications, however it looks like it's time again for my opinion on what seems to be an annual 'is salt water a chemical transfer' debate'. Here's my post from last year (http://scioly.org/phpBB3/viewtopic.php? ... al#p253500) about this:

Hmm. It's not so clear cut. From Wikipedia( http://en.wikipedia.org/wiki/Sodium_chloride):

"The attraction between the Na+ and Cl− ions in the solid is so strong that only highly polar solvents like water dissolve NaCl well. When dissolved in water, the sodium chloride framework disintegrates as the Na+ and Cl− ions become surrounded by the polar water molecules. These solutions consist of metal aquo complex with the formula [Na(H2O)8]+, with the Na-O distance of 250 pm. The chloride ions are also strongly solvated, each being surrounded by an average of 6 molecules of water.[4] Solutions of sodium chloride have very different properties from pure water."

Now there is indeed debate over whether this is a 'physical' or 'chemical' reaction (just do a google search for 'Is dissolving salt in water a chemical or physical reaction'). In fact, Wikipedia, as usual, provides a good summary of the source of the confusion (http://en.wikipedia.org/wiki/Physical_reaction):

"Many chemical changes are irreversible, and many physical changes are reversible, but reversibility is not a certain criterion for classification. Although chemical changes may be recognized by an indication such as odor, color change, or production of a gas, every one of these indicators can result from physical change"

However, looking at the rules closely, note they don't say the words 'chemical reaction' anywhere. They refer to 'the 5 basic energy forms', which infers that all possible tasks can be classified as one of the five. Thus in my opinion (which is unofficial as always) if someone doesn't want to classify salt into water as allowable for the chemical energy form, they need to make a strong argument as to which of the other forms it should be classified as instead.

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Re: Energy Transfers

Post by goodcheer »

torqueburner wrote:
I would say that dissolving NaCl in water is a physical change, not a chemical change. I spoke to our current and past high school chemistry teachers, who both confirmed this. A quick on-line search finds many others who agree, including:

http://chemistry.about.com/od/matter/a/ ... Change.htm
Checking the sources you listed, notice the very first one is from a PhD Chemistry Expert who says, "dissolving salt in water is an example of a chemical change." That is also my opinion on the matter; however, as indicated, this is considered a gray area among chemists. Anyhow, the discussion as to whether this is a chemical or physical change seems to be moot with regards to this being a transfer step in an ETS for Mission Possible.

To expand upon Chalker's comments, the purpose of the salt solution is not to create a chemical change or reaction, but simply to turn on a switch to allow electrical current to flow. The current flows through a chemical solution containing water, Na ions, and Cl ions. That's why it is accurate to say the solution acts like a chemical switch and therefore a transfer occurs from chemical to electrical (C-E). Ask the chemistry teachers if a mixture of salt and water is a chemical solution or not.

If someone wants to avoid the possibility of this not counting as an ETS, you might want to try some other chemicals that will also cause electrical current to flow. For example, adding ammonia to vinegar should work. More care should be used in handling these chemicals (don't sniff the ammonia or vinegar). It would be hard to argue this is not a chemical transfer (C-E), although the same concept is seen with the solution of salt water.

Source: http://lecturedemos.chem.umass.edu/chem ... ns4_7.html
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Re: Energy Transfers

Post by wlmeng11 »

My chemistry textbook ("Chemistry: The Central Science" by Brown et al) says dissolution of salt in water is a physical change. However, conducting electricity through salt water does cause an electrolysis reaction which is certainly a chemical change: 2NaCl(aq)+2H2O(l) --> 2Na+(aq)+2OH-(aq)+Cl2(g)+H2(g)

So dropping salt into water to complete a circuit should count as C-E :)
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Re: Energy Transfers

Post by bernard »

wlmeng11 wrote:My chemistry textbook ("Chemistry: The Central Science" by Brown et al) says dissolution of salt in water is a physical change. However, conducting electricity through salt water does cause an electrolysis reaction which is certainly a chemical change: 2NaCl(aq)+2H2O(l) --> 2Na+(aq)+2OH-(aq)+Cl2(g)+H2(g)

So dropping salt into water to complete a circuit should count as C-E :)
I listed dissolution of salt and electrolysis as C-E last year and didn't have any problems with incorrectly listed transfers, so this is correct!
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