8 ms·
Just curious, how else can mass be converted to energy? EDIT/replying: I'm inclined to continue to believe that it can't in any other way. 1. Not through a c
by ihodes 11y ago
Just curious, how else can mass be converted to energy?
EDIT/replying:
I'm inclined to continue to believe that it can't in any other way.
1. Not through a chemical reaction; energy can be released in a chemical reaction, but the total mass/atoms involved remains the same.
2. Not through kinetics; energy can be produced, but mass remains the same as well.
cf. some interesting caveats here http://en.wikipedia.org/wiki/Conservation_of_mass http://en.wikipedia.org/wiki/Conservation_of_mass
- glomph 11y agoAny chemical reaction?
- bobowzki 11y agoNo mass is lost in a chemical reaction.
- msandford 11y agoSpeaking in generalities yes, but TECHNICALLY stuff that contains more energy is heavier too. But given that most enthalpies are in the kJ/mole range and most moles of things are pretty heavy relative to 9e18 (the speed of light squared) that you might as well round it out and say "no mass is created or destroyed in an ordinary chemical reaction"
- peterfirefly 11y ago2H₂ + O₂ --> 2H₂O + Q Q is the released energy. If you weigh the molecules before and after very carefully, you will notice that they lose weight (or mass if you are being pedantic about it). That mass loss corresponds exactly to the Q-value (through E=mc²).
- MarcScott 11y agoNo mass is lost in this reaction. The mass of the atoms remains the same. The energy that is released is due to the difference in bond energies. To balance the equation you would need to add a Q to the other side, corresponding to the bond energies.
- sp332 11y agoThe energy Q is in the molecules. It is released during the chemical reaction.
- MarcScott 11y agoThe molecules consist of Hydrogen and Oxygen that have equal atomic masses, either side of the equation, due to the identical numbers of protons, neutrons and electrons. Any mass gained or lost will be due to changes in bond energies, and the corresponding emission or absorption of photons that change the energy states of the electrons in the bonds.
- dietrichepp 11y agoPutting a Q on the left hand side would be an error. Q indicates that the energy is not bound in the molecular configurations. If you measure the mass of a quantity of water accurately enough, the mass will be lower than the mass of the equivalent amount of hydrogen and oxygen gas. The difference would be so small that our most sensitive instruments would not be able to detect it. Likewise, in a nuclear reaction, the only thing changing is the nuclear binding energies of the protons and neutrons. However, since the energy involved is many orders of magnitude higher, our instruments are sensitive enough to detect the difference in mass.
- fluidcruft 11y agoWhy is Q not part of the system anymore? Isn't the Q carried by the 2H₂O molecules (or the solution/matrix/whatever)? Doesn't it just represent that the energy is of a different form?
- dragonwriter 11y agoIts part of the system, but its not mass anymore but another form of energy. Mass is lost, energy is conserved.
- fluidcruft 11y agoHow does bond energy represent mass but kinetic energy does not represent mass? I realize Q is a different symbol in the formula, but that's just notation. The bond energies are implicit in the formula, but that doesn't mean they aren't there.
- Pyxl101 11y agoNot technically correct. A small amount of mass is lost or gained in chemical reactions, just like when gravitational potential energy is gained or lost. If you walk up a flight of stairs, you will be heavier at the top. If an electron changes orbital, its mass changes as well, making it heavier or lighter. Let's calculate it. A 90 kilogram man walks up a flight of stairs, one story (3.3 meters). The expression "m * g * h" gives us the gravitational potential energy of mass "m" ascending height "h". Evaluating the formula we get 2910 joules. So how much heavier has the man become? Given E=mc^2, then m = E/c^2. As you can see, we'll be dividing by c^2, which is a very big number. The resulting increase of mass is 3.24 E-14 kg, or too small to be noticeable, but still very real: A 90 kg man ascending a 3.3 meters gains 0.00000000000003 kilograms of mass. Chemical potential energy changes result in mass changes as well. These changes in mass are insignificant at the scale of chemical reasons, but are indeed taking place. So while it may be reasonable to simplify a discussion of chemistry by saying that chemical reactions don't change mass, in reality the changes do take place, just at a very small scale. A starting point for further research: "Whenever any type of energy is removed from a system, the mass associated with the energy is also removed, and the system therefore loses mass. This mass defect in the system may be simply calculated as Δm = ΔE/c^2" https://en.wikipedia.org/wiki/Mass%E2%80%93energy_equivalence#Binding_energy_and_the_.22mass_defect.22 https://en.wikipedia.org/wiki/Mass%E2%80%93energy_equivalenc...
- mindslight 11y agonit: "heavier" refers to weight, not mass. The man will actually be lighter at the top of the stairs due to decreased gravity. (R_earth / (3.3m+R_earth))² ≈ -0.0001 % Someone else can calculate the decreased buoyancy in thinner air ;)
- thaumasiotes 11y agoHuh? What chemical reaction has less mass afterward than beforehand?
- peterfirefly 11y agoAll exothermic ones?
- sp332 11y agoWell it has less mass-energy total, but the energy is in chemical bonds that are made or broken. You have the same amount of mass in there though.
- TeMPOraL 11y agoPer E=mc^2, energy and mass are basically the same thing. Also, if you weight your substrates before and after and exothermic reaction, you'll see a (very tiny) loss of mass.
- sp332 11y agoYeah I know they're basically the same which is what makes this hard. And energy stored in chemical bonds has gravity just like some tiny amount of mass would. But if someone is asking for the difference between mass and energy, I wouldn't put that on the mass side.
- peterfirefly 11y agoAre you just humptydumptying me or do you actually think of in terms of "same amount of mass"?
- deleted 11y ago[deleted]
- inyorgroove 11y agoThere are several ways that "mass" can be converted into energy. In this case we are not talking about e=mc^2. The conversion of fat cells to energy for brain and muscles should involve at the end of the day: urine (lactic acid etc.) and exhaled H2O and CO2. Edit: Notice I put mass in quotation marks. I am not trying to break the law of conservation of mass. Fat cells consumed will produce energy through some kind of biological process.
- fluidcruft 11y ago...isn't that just re-arranging atoms and electrons into lower energy states? The mass of those atoms and electrons doesn't change. A block of steel has the same mass at the top and bottom of a hill.
- deleted 11y ago[deleted]
- TeMPOraL 11y agoIf that block is falling down then it's actually little heavier at the bottom, by E_k/c^2, where E_k is its kinetic energy.
- dietrichepp 11y ago> A block of steel has the same mass at the top and bottom of a hill. This is only approximately true. It would be hard to measure the difference, for sure. Relativity gives a lot of seemingly bizarre results: * If you carry something uphill, it gains mass as you go. (Kind of... consider that it is part of a system which includes the Earth.) * If you compress a spring, it gains mass. * If you charge a battery, it gains mass. * If you fire a laser into space, it will have a longer wavelength when it gets there. * If you hook a shaft from the ground into space and turn it, it will turn faster at the bottom and slower at the top. We live in the "middle ground" which is well approximated by Newton's laws. Strictly speaking, Newton's laws are false.
- fluidcruft 11y ago
- sp332 11y agoParticles can decay into other kinds of particles. It doesn't have to be nuclear fusion or fission.
- kabouseng 11y agoRadioactive decay is still a nuclear reaction though...
- nordsieck 11y agoThe mass of a molecule is the mass of its constituent atoms plus the mass of the bonds between them. When those bonds are broken, the system loses the amount of mass one would expect given e = mc^2. Note: this amount of mass is very small and so is typically left out of introductory chemistry courses.
- gus_massa 11y agoThe mass is almost almost almost conserved in chemical reactions. By special relativity, the energy/heat that produces the reaction should come from a extremely slightly difference of mass between the reagents and the products. The difference is so small that in any chemical class and chemical application you just assume that they are equal. (http://en.wikipedia.org/wiki/Conservation_of_mass#The_mass_associated_with_chemical_amounts_of_energy_is_too_small_to_measure http://en.wikipedia.org/wiki/Conservation_of_mass#The_mass_a... ) For example, a person consumes approximately 2000 kcal/day of food. The calculation is more complicated, because not all the energy is used. But for the sake of the argument, let's assume that the person just use all the 2000 kcal and they are lost as heat, work (lifting a heavy object , moving the air, moving the water while swimming, ... ) Using the famous E=mc^2 equation we have that m=2000 kcal/c^2 = 9E-8 grams = 3E-9 ounces. That's very small and is not useful for a diet, but it's not zero.