Timeline for Conversion of mass to energy in chemical/nuclear reactions
Current License: CC BY-SA 3.0
11 events
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| May 14, 2013 at 20:05 | comment | added | dmckee --- ex-moderator kitten | The mass changes related to chemical processes are negligible for all practical purposes (and many impractical ones), but I don't think it serves to draw a false distinction here. Your instructors are right to ignore this detail on the first pass through the material, but it should be understood that as with the many other approximations that are made at first this is sacrificing correctness for simplicity. | |
| Jul 1, 2011 at 22:21 | comment | added | Vintage | @zephyr - I don't feel like my high school and college chemistry and physics teachers were lying or holding out on me or doing me a disservice, and none of them mentioned this to me. They all, of one accord, emphasized that there is no mass loss in a chemical reaction. I see your point. I hope you see mine. | |
| Jun 28, 2011 at 3:45 | comment | added | user2963 | @Vintage - it is misleading because it ignores the universality of the process. There is a mass loss in a nuclear reaction and a chemical reaction, it is only the magnitude that differs. The physics is exactly the same. This is not a philosophical position, it is a straightforward application of our currently known laws of physics. There are many implications of these laws which can be neglected in the practical world, that does not make them any less real or true, and you do a disservice to learners by dismissing the truth rather than seeing the unified whole. | |
| Jun 27, 2011 at 17:44 | comment | added | Vintage | @zephyr: What is false and misleading about the answer? If you react a mole of A with weight X, and two moles of B with weight 2Y, you get a mole of AB2, with weight Z. If you look up these weights you find that X+2Y = Z. So where is the lost mass? The next thing you'll be telling me is that a baseball thrown to me is lighter after I catch it. You might think Einstein makes you right; but if even the smell of my glove or hand gets on the ball. you are certainly wrong. In any case, in the practical world such a position is worthless. Same story for the chemical reaction. | |
| Jun 26, 2011 at 13:09 | comment | added | user2963 | @Vintage: fair enough, if you want to promulgate a false and misleading idea that's your right. If you want to understand the truth here's some pointers: Einstein gave us the famous equation equating mass and energy. A chemical reaction, considering only the atoms/molecules of reactants and products is not a closed system: the products will be in an excited state and will release photons to the environment as they relax to thermal equilibrium. These photons have an associated 'mass'. Where did this come from? | |
| Jun 23, 2011 at 21:21 | comment | added | David Z | @Vintage: fair enough. | |
| Jun 23, 2011 at 20:18 | comment | added | Vintage | @David. Thank you for the tip. I'll stick with my answer, though, downrated as it is. I don't see anything in it that is untrue, in the classical mechanics sense. If someone were to tell me that mass is lost or gained in a chemical reaction, I'd respond, "How much mass?" If they tell me they are not sure, or can't even measure it, then I'd respond that my answer is perfectly fine in the practical world. Sort of reminds me of Pluto: It's not a planet anymore, but it was 10 years ago. Makes me wonder if it was really a planet when science said it was a planet. What changed on Pluto? | |
| Jun 23, 2011 at 0:12 | comment | added | David Z | @Vintage: just in case you didn't know, if you realize that an answer you posted is wrong, you should be able to delete it. Of course you're not obligated to do so. | |
| Jun 23, 2011 at 0:11 | comment | added | David Z | @zephyr: not everyone knows everything. I don't think we need to discourage people from posting answers even if they aren't completely sure; the risk of getting downvoted should be enough to do that. | |
| Jun 22, 2011 at 20:57 | history | edited | Vintage | CC BY-SA 3.0 |
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| Jun 22, 2011 at 20:31 | history | answered | Vintage | CC BY-SA 3.0 |