BrainQuest!
 

Anyone remember this game? It was a fairly early educational series that made being smart "cool". Anywho, I was cleaning out the closet and found some cards, with questions I disagree with. What's your take?

True or false? Adding salt to a pot of water makes it reach the boiling point faster. True

Erm, adding solutes does affect the boiling/freeezing point, but by making them higher/lower respectively. Which would technically make it reach the BP later, right?

In which of these states is matter heaviest: solid, liquid or gas? Solid

Weight is determined by mass*gravity. In transition between phases, matter is not lost. So if both matter and gravity are constants, then so is weight.

Aaah, so we were more ignoarant back then ;)
Not sure about the first one, way too rusty on that.. but the second definetely seems untrue to me.. and pretty obviously, too...
*Hoping I didn't just miss an opportunity to shut up*

OK , I tested the boiling question. Without salt. it took my electric stove set on high. 2,54 mintues to boil 2 cups of water. using a different burner, pot, the same amout of water (2 cups) added one tsp of salt. It took 2.4 mintues to reach boiling point. Not a great differenace. but still a differance

as for the mass question. That's a little bit more tricky. the mass is the same. this is true. however the particles are so spaced out in the container that it effects the weight. so the truth should hold the same for liquid. I would have to do more research to confirm it though.

nice idea for a thread. thanks

A pound of ice weighs the same as a pound of water, no? (Or, if you're not an American, use the far superior metric system)

As far as your experiment, that's pretty interesting. Although did you make sure the burner cooled off completely before boiling again? Whatever, my Chem teacher is gonna hear about this tomorrow. :)

Now, let's not start that again :D

Correct. a pound of water should weigh the same. But if that water was steam? how would it weigh? Gas have a very low density because the particles are so spaced out in the container.

And yes. I used a completely different burner, pot, water, everything.

Well, I found the reason for the boiling point question:

still working on the weight/mass thingy

It shouldn't make the slightest bit of difference. Gravity is constant, right? And when the water boils into steam, matter is conserved, right? So we have constant mass and constant gravity. There are only three terms in the formula weight=mass*gravity. So weight must be constant as well. Just because it's a gas doesn't mean that it has any less weight. The particles just have too much kinetic energy to settle into a solid/liquid.

Oh, and I knew why solutes raised/lowered BP/FP, I was wondering how they could make something boil faster. That quote agrees with me that it would take more energy. So it boils faster because it needs more energy to boil? :confused:

Bah, I can imagine some copy writer somewhere going "Hey WTF? I was just paid to type this shit!" Salt would raise the boiling point, boiling it slower. The mass of a material is the same, whatever state it is in. The apparent weight might be different if you take into account it's bouyancy and relative densitiy to air (assuming you are weighing it in air, steam might be apparently lighter than water/ice due to it's relative density) Strange thing about water of course, is that in it's solid form, it's actually less dense than it is in it's liquid form (the reason ice floats), so if relative bouyancy is at issue, and if the material is water, then the answer would be liquid. But like I said, hack writer + one too many pulls on the bottle = crappy questions

What's heavier? A pound of feathers, or a pound of bricks?

neither, a pound is a pound. which is what the whole debate about which is heavier, solid, liquid, or gas.

In the presence of a constant gravitational force, constant mass implies constant weight. Weight has nothing to do with density. Nothing. None.
Boyance is a separate issue from weight.

EDIT: quoted for great justice
from above.
The boiling temperature increases. High school chemistry tells us that solutes increase boiling point and lower freezing point. That's why cooks put salt in their water when they're boiling stuff, and why homeowners go out and buy bags of salt for their driveways.

Of course, they were thinking "density" when they wrote the question, not "mass", but even if they wrote it correctly, the question remains a bad one. Ice (solid) floats on water (liquid), and is therefore less dense.

EDIT: zen_tom already mentioned this in his post, but I missed it on my first read, so I'll keep my post up here to make the point more obvious.

Right, adding salt increases boiling point, and ICER gives a good explanation.

However, the question is only talking about reaching the bp, not what the bp itself is. And I'd agree with you that with a higher bp, it would take a longer time to heat the water. Which then confuses me, because when cooking pasta, you sometimes add a pinch of salt, which people say makes the water boil faster. I think this is where this question comes from.

I've googled it, and one possible answer is that the salt provides nucleation sites for the water to start boiling, but this seems unlikely because salt is soluble in water, and you would need larger insoluble particles for nucleation sites. My only other guess is that the salt affects the specific heat but i don't know enough about those thermodynamics to say anything definite, and my instinct says that it can't affect it by much...

Just as a follow-up, I asked my Chem teacher today. She confirmed that all phases weigh the same, and the BP should logically take longer to reach. She did say something about salt and bubbles that might affect the BP, but I didn't really catch it. And she said it was unlikely. So there, teach says so. :p

Good enough for me :thumbsup:

So, what have we learned.

1: Don't buy a Brain Quest for your kids
2: a pound is a pound.
3: Always listen to the teach (unless you want to fail)

And I goofed on the boiling test. Although I used exact amounts in both pots. The second pot was a few inches smaller and had a wider bottom. allowing the water to heat up faster. :| (hate it when that happens)

Eh, there were hundreds of cards, each with 6 questions. Typos (while annoying) happen.
:mad: Blargh. Oh well, that's what the scientific method and structured experiments are there to prevent, right? No hard feelings.

In which of these states is matter heaviest: solid, liquid or gas? Solid

If we assume that we are talking about the same material, wouldn't the gas weigh the most and the solid the least, with the liquid in the middle? Given that the mass is the same the only difference between them would be the amount of energy they contain, and the gas would have the most.

Phage, keep your terms consistent.

Mass
Volume
Weight: force, or mass times gravity (which can be considered a constant, so weight is another way of saying mass)
Density: mass divided by volume

My terms are consistent; when I said weight I was talking about the weight, and when I said mass I was talking about mass. I did not mention volume or density because they have no bearing on weight, which was what the question was about. My point is that the extra energy required to change the solid or liquid into a gas would result in an increase in mass and thus weight.

Hmm, missed that, sorry. But, I don't think that adding heat energy increases the mass; does it? It's been quite a while since I've taken either chemistry or physics.

No. The energy that changes the liquid into a gas or any other phase change goes into making the molecules move faster. Einstein's E=mc^2 (where mass and energy can be interconverted) has no bearing on this question.

You are correct in both analyses. It would take longer for the water to boil, and the weight = m*g or the mass alone would be constant regardless of the phase of the compound. I have a Ph.D. in chemistry.

Ok...so not until May...but good enough :)

These two links refer to what I am speaking about specifically:
http://dbhs.wvusd.k12.ca.us/webdocs/...ss-Energy.html
http://van.hep.uiuc.edu/van/qa/secti...0923112019.htm

...while this one is just good reading.
http://en.wikipedia.org/wiki/Conservation_of_mass

"The law of conservation of mass states that the mass of an isolated system will always remain constant, regardless of the processes acting inside the system."

Suppose that we use our handy-dandy e=MC^2 formula on an isolated system which is one cubic foot in size, and convert 1 gram of a 5 gram block of iron directly into energy. What you have just suggested is that the mass of the closed system will be reduced by this change, which is clearly in violation of the Law of Conservation of Mass. By extension we must conclude that because energy has mass (even though a gram of energy would be quite a lot) adding it into a closed system would increase the mass of that system.

I read your links... and I have to say that this is the first time I have ever heard of energy having mass.

yeah, that's a new one on me too. Interesting concept though. Does energy exist as mass at the atomic level, or is it nothing more then a radiation that excite particles to become energy.

Well Energy itself doesn't have mass per se , but as the first link points out, it is possible under certain circumstances to interconvert mass and energy. That's where E=mc^2 comes in.

When the US was testing out its atom bombs in WW2, they showed that some mass was lost, and transformed into energy (just a little, not all the energy of the bomb). They did the calculations and the data fit E=mc^2 rather well

hehe. You changed too many variables. How do you know the 2nd burner gets to the same temperature? How do you know the 2nd pot conducts heat the same as the first one. What you needed to do was to turn the burner on for say 15 minutes to guarantee it was at max temperature. Then put the pot with the fresh water and time it. Then empty the pot, and wait for it to cool to room temperature. Then put saltwater in it and put it over the same burner, which you have either not turned off or have turned on 15 minutes previously.

That would be much more accurate, though still poor in accuracy because electric stoves don't maintain a constant temperature unlike gas.

As I have said before mass must be conserved, so if it is possible to convert matter into energy then it must follow that the energy released has mass. Yes, it per se has mass. The testing by the US would have found out that some matter was converted to energy, instead of showing a mass loss and refuting basic concepts of thermodynamics.

Correct me if I'm wrong, But don't we covert matter into energy everytime we set a log on fire? I mean the fire consumes the log, giving off heat energy right?

Combustion is not a matter to energy conversion but merely a vigerous oxidation reaction. It releases the energy stored in the chemical bonds of the wood, but all of the matter is still around in some form.

I am unsure about hte salt off the top of my head, however with the second question it should read something to the degree of per cubic meter. In which case everything but water as far as we can tell would agree with the statement. However, water being as it is, expands upon becoming a solid therefore when water is a liquid it "weighs" (or contains more of itself) inside a cubic meter. However if the question is really as simple as it is stated then the only answer is nothing.

I am speaking on no authority here, but I believe that the first question is correct and that the saline solution will have broken apart the water molecules therefore needing less energy to seperate them into a vapor. I know one of the complex parts about sperating water is their shifting hydrogen bonds. As a matter of fact it is nigh impossible for a computer to model even five water molecules interactions in real time.

Damn you Phage. I had a nice short essay about E=MC^2 and how it meant that turning an amount of solid into a gas resulted in something that weighed more.

Then I read more of the thread, and you had already done it. Better than my essay too!

Humbug! Ruined my fun. I do have one thing to add:

The amount of mass (and hence weight) added by taking a solid and turning it into a gas is so small I personally doubt it would be measureable.

If you took a cube 10 m on each side, weighing about 1000 tonnes, and turned it into water vapour, the resulting gas would have about 36 miligrams more mass than the original ice cube.

As an aside, the energy in a 1 megaton (H-bomb size) nuclear explosion comes to about 47 grams of mass. The energy in the tsunami in SE asia massed a quarter of a kilogram. The energy in the earthquake that triggered it massed between 10 and 100 kg.

Another fun thing: if you took a cube of water, 30 km on each side, and turned it completely into energy, you would have about enough energy to push the earth into the sun.

In what way?
I ask because I've modeled upwards of several million gold, nickel, and copper atoms in nanoindentation simulations. You'd be surprised at what a modern supercomputer can do.
EDIT: I can't type.
EDIT2: nor can I spell

Maybe they meant to say most dense? That'd be pretty legit then.

WHAT??? Why would you convert mass into energy with a simple phase change? I'd really like to see your calculations.

It's possible he means in a fully thorough, quantum mechanics sort of way. I know that even for something as simple as a hydrogen atom, or a helium molecule, the math is pretty involved, so i can only imagine what it's like for one, much less 5 water molecules

I calculated how much energy it would take to turn a 10 m cube of ice into water vapour. Somewhere around 700 calories/gram.

I then divided by c^2, and got the mass of that energy. Remember, all energy has mass.

Thus, if you take a block of ice, and turn it into water vapour, the resulting water vapour will mass more (and hence be heavier) than the original block of ice, but only by a very small amount.

That is based on the assumption that all the energy is contributed to an increase in mass, which is wrong. Energy does not get converted to mass in a simple phase change. Any energy you put into the system goes into the thermal energy in the water to increase temperature and boil it. But that energy does NOT go into a mass increase.

I still maintain that all energy does NOT have a mass. Take a 1kg block and drop it from a height of 1m. When it hits the ground it will have approximately 9.8Joules of energy, but the energy does not go into increasing the mass.

Likewise, an exothermic reaction releases energy due to a difference in Gibbs free energy. The difference in energy in the chemical bonds that make up the molecules of the reactants and products is responsible for this. But no mass is converted into energy or vice versa.

I'll agree to the statement that a given amount of energy can be associated with a given mass, according to E=mc^2. But energy does not have mass.

How then do you reconcile a conversion of matter to energy in a closed system without violating thermodynamics? Where did the mass go?

It turned into energy. I might be wrong, but I think this might be quantum mechanics, which doesn't exactly follow every rule.

Did you look at my links earlier in the thread?
Can you give some justification for saying that the Law of Conservation of Mass does not apply, or why such a reaction would not follow the rules of Thermodynamics and instead would be described by a system without definite rules?

Your last post seems to be in essence "I don't like the rule that you cited, so instead I think I will apply a different system in which I don't have to follow rules."

Well, there is a bit of confusion.

First of all, both Phage and I are not talking about "rest mass". Photons do not have rest mass.

Good old Baryonic Matter has rest mass. Photons do have mass, but no "rest mass".

If you heat up Baryonic Matter, it's "rest mass" doesn't increase. But, it's mass does.

If you add energy to a system, the system will generate more gravitational force (gravitational mass), and will have a higher inertial mass (it will be 'harder' to change it's velocity).

Energy is not a thing. Energy is not a particle, it's not a force. Energy is a property of matter, kinda like color. Energy, being a property of matter, cannot have mass. It's like saying the color blue has mass. It makes no sense. Energy is a term that we use to describe a specific property of matter, and obeys certain conservation laws.

Conservation of Mass is not a universal law. The correct themodynamic law is conservation of Energy (1st law). Mass conservation only applies when you are dealing with classical physics, like balls colliding or chemistry. Mass conservation fails when you start dealing with relativity and nuclear reactions.

It is possible to change mass into energy. The atomic bomb, for instance, does just that. It takes some mass from the plutonium/uranium and converts that mass into energy which we then feel as 1) light 2) heat 3) shock waves. (Remember, we don't feel the energy directly, energy is a property of matter)

It is possible to convert energy into mass. A photon, which has no rest mass, of a high enough energy (say a gamma ray) can spontaneously convert itself into an electron/positron pair. This process is called pair production. Where you had zero rest mass before hand, you now have a mass of 2 Me (electron mass). Hence, we say that Mass Conservation is not a Universal Law, it's scope is limited to classical physics.
(well, I suppose you could use E=MC^2 to calculate the mass equivilance of all energy and say that mass is constant, instead of energy, but that would be silly and none in physics would do that.)

The statement E=MC^2 is an equivilance statement. X amount of energy is equal to Y amount of mass. It doesn't mean that energy has mass, or mass has energy (it's like saying Red has Shiny. It makes no sense). Mass and energy are both properties of matter. It simply means that these two properties are equivilant under certain contexts.

Edit: Positron, not proton. oops

The laws of thermodynamics are as follows:
0th law: Transitive Law. If A is in thermodynamic equlibrium with B (A=B), and B is in thermodynamic equlibrium with C (B=C), then A is also in thermodynamic equilibrium with C (A=C). Basically, this means, if A and B have the same temperature, and B and C have the same temperature, A and C have the same temperature.

1st Law: Energy Conservation. In a closed system, Energy is conerved. or U=Q + W. The energy of the system is equal to the heat of the system plus the work done on/by the system. (U= total internal energy, Q = heat, W = work)

2nd Law: Entropy always increases or stays the same. For any spontaneous process, the associated Entropy change is always positive. For a quasistatic process (if I move things infinitesimally slowly), the entropy change may be zero.

3rd Law: Temperature approaches absolute zero assumptotically. You can never reach absolute zero, and you can never have a true quasistatic process. Thus, entropy always increases, and at some point, heat will be so evenly distributed across the universe, that there will be no spatial gradient to the heat, thus no more usable energy (heat death of the universe).

If I meant to say that Energy has "rest mass", I would have said "rest mass".

Instead, I said:
Photons have mass. They have no rest mass. All energy, no matter what form, has mass.

If you take two atoms that each weigh X, and bind them together so that Y energy is absorbed by the breaking of the bond, the resulting molecule will have (2X-Y/c^2) mass.

If you take a proton and a neutron that weigh P and N, and you bind them together such that Z energy is absorbed by breaking their bond, the resulting atom will have (P+N-Z/c^2) mass.

You heat something up, the same amount of matter will now have an extremely small increase in the amount it bends space and how hard it is to change it's velocity. Otherwise known as it's mass.

As an aside, fckm, you forgot 'in a closed system' requirements in your 2nd law.

The moclecule has mass.

The atom has mass.

That something, has mass.

See the pattern here? The property, _Mass_, is a characteristic of the material you are talking about. The property, _Energy_, is also a characteristic of the material you are talking about. The property, _Mass_, is not a characteristic of the property, _Energy_. Again, Atom, Molecules, Photons, My beer gut, all have mass. They also all have energy.

Energy doesn't have mass. Energy is not a thing. Energy cannot have mass, because Energy itself is a characteristic of some material. It cannot, it does not, exist independantly of matter.

My beer belly can have Energy. The more Energy my beer belly gets, the more inertial Mass it obtains. It's not the Energy that "has mass", it's my beer belly. It's not the energy that has mass, it's the molecule. It's not the energy of a nulcear bond, it's the atom that has mass.
Only things can have mass. Energy isn't a thing, it's not a particle, it's not some object, it's a property of matter. It doesn't make any sense to say "Blue has Shiny", so it doesn't make any sense to say "Energy has Mass".

Ah yes. Thanks for pointing that out. Oops.

The reason I'm being so pedantic here, is because of the thread in Philosophy, titled E=MC^2, discussing beings made of energy. I just want to make it clear that energy isn't a thing, it's a property.

Edit: more clarity?
Edit2:

I'm quoting myself for emphasis here.

Well, if you had read my earlier posts, you would see that I did read your links. What I failed to convey was that the laws of conservation of mass/energy only work in classical physics. fckm has done a much better job.

Is a Photon Matter? Or, are you asserting a Photon cannot exist without Matter? That's getting pretty obtuse. Gravaton?

Because, Photon's aren't very "Matter"-like, and they contain Energy (and hence have Mass).

(ok ok, Non-Baryonic matter. Meh, not very Matter-esque!)

How about Negative Energy Fields? I think it is believed they have negative mass. (you can apparenly build them by placing two metal plates very close together in a vacuum -- between the plates, you end up with something that is more empty than a vacuum.)

Are Negative Energy Fields matter? (I suppose you can renormalize the universe, so hard vacuum isn't at zero, and thus make 'Negative Energy Fields' just 'a place with less stuff than a hard vacuum')

Being further pedantic, I think I can build a non-bounded universe model in which heat-death never occurs. So, your conclusion you rolled into the 3rd law isn't derivable from the 0th, 1st 2nd and 3rd laws of thermodynamics. In order to do this, I think I need negative enthropy systems (which isn't ruled out by the 0th, 1st, 2nd or 3rd law).

Build a universe model where the total enthropy is unboundedly negative, but for all compact subsets of the universe it is bounded. You end up with a universe that looks like ours does locally, but possibly never reaches heat death (there is always some point that is hotter than others by as any margin you want).

I don't know what "negative enthropy" systems would look like.

Measuring energy as mass has some nice properties. It does away with two extra units: distance and time are no longer "dimensions" to your energy unit.

The photon has 2*10^-16 kg of Energy.
We provided 2*10^-20 kg of heat to the water.
The bomb blast was 2.5 * 10^-1 kg of Energy! (5 megatonnes, if I did my math right)

It is sort of like measuring distance as time, or time as distance. Once you have a nice conversion factor (c), keeping track of both units seems silly.

I think this is a philosophical position, or a convention, not a scientific statement.

If you interprited Energy as the thing (maybe the only thing!) that has Mass, and note that all Matter has Rest Energy, you should be able to do the exact same physics. Just with slightly different translations into English.

Hell, you could say that Energy is the only thing, and that it "must" have Matter (instead of Matter "must" have Energy).

Slavakion, from what I can tell, Fckm was mostly disagreeing with terminology.

I don't believe Fckm disagrees with the statement "the gravitational and inertial mass of a closed system is constant". Which means melting an icecube results in water that weighs more than the ice cube did, by an increadibly small amount.

I like to think of matter as anything that's defined as being a particle in the current Standard Model.

I'm an engineer, not a theorist, so this is currently beyond me. But here's a good article about the Casimir effect:
http://physicsweb.org/articles/world/15/9/6
Notice that all fields being refered to are still EM fields, which , I believe, still have to be quantized as photons.

I'm not sure about this. I don't think it would be very useful, since most physics work is done in energy. In fact, it's far more common to use energy units to measure mass, than to use mass units to measure energy.

Except that in a historical context (and a teaching context), classical physics came first. Also, I'm not sure how the Higgs boson fits into all this. (I'm an engineer, not a theorist).

yup
I agree, although the amount is so small, it's not measureable.

After thinking about it, I guess it makes sense that if a little bit of mass contains a huge amount of energy, a huge amount of energy contains a little bit of mass. That's still thinking about it in terms of e=mc^2, though. *shrug*

This has been a fascinating read. I think that gases *would* gain a small amount of mass over solids. I'll have to debate this one with my physics friends and see what they think.