What are the positive human impacts on energy conservation?

conservation of mass+energy

• http://www.appliedthought.com/InsightPress/ThinkSample.html gives a sample question from the book 'Thinking Physics': Which of the following statements is correct? (a) E=mc^2 tells us how much mass loss, m, must be suffered by a flashlight battery when the flashlight puts out a given amount of energy, E. (b) E=mc^2 applies to nuclear energy in a reactor, but not to chemical energy in a battery The answer is given ( http://www.appliedthought.com/InsightPress/EmcAnswer.html ) as (a). This seems wrong to me. I thought that nuclear reactions actually convert mass to energy, whereas chemical reactions merely rearrange mass into higher or lower entropy (potential chemical energy) forms. It seems to me that their example violates conservation - the mass lost doesn't "go" anywhere, it is *converted* to energy! The total mass+energy of the system remains constant. Please provide a detailed explanation of either why I'm wrong or right.

• Answer:

  Wow. I like to think I learn something everyday, and I usually do. But it rare that I learn something so contrary to everything I had learned earlier. My answer to the question would have been the same as yours. It makes perfect sense -- and besides, that's always what I had been told. But now that I think about it, answer B does make sense. The key is that the amount of mass loss is so incredibly tiny that for all practical purposes there is no mass loss -- certainly nothing you nor I could measure. Nowadays, as a matter of fact, the law of conservation of mass is worded to say that there is no detectable (note that word) loss or gain of mass in a chemical reaction. Here's another way it's described: Conservation of Mass in Chemical Reactions "In chemical processes, the most important property to be conserved is the number of atoms of each kind that are present. Unlike nuclear processes, chemical reactions do not create or destroy atoms, or change one kind of atom into another. They only reshuffle the atoms that were originally present into different molecular combinations. What we would like to be able to do is to count each kind of atom before and after a reaction and make sure that none has been gained or lost. "Counting atoms directly is not practical, but because mass-energy conversion is NEGLIGIBLE in chemical reactions, conservation of the number of atoms effectively means the conservation of mass." [emphasis added] http://www.chem.ox.ac.uk/vrchemistry/Conservation/page07.htm One theoretical explanation is on that page you provided a link to. Similarly, imagine a flashlight in outer space emitting light (or a satellite emitting electromagnetic energy) while powered by a battery. The device is receiving no energy (we'll assume it's in complete shade), yet it's emitting energy. Where's that energy coming from? It can't be getting energy from nothing. The answer is that Einstein's formula (E=mc^2) applies. A tiny amount of mass is being converted to energy in order to balance that formula. In other words, if a closed system is producing energy, it must be coming from mass for Einstein's formula to hold true. How tiny is the loss of mass? The following page has the answer: Conservation of Mass, Charge, and Energy "In principle, if a reaction gives off energy, the products formed must have lower energy and be lighter than the reactants. But a release of 100 kcal mole^-1 by a typical chemical reaction corresponds (via the Einstein relationship) to a mass loss of only 5 x 10^-9 amu per molecule, or one hundred thousandth the mass of an electron. This amounts to only 5 x 10^-9 gram per mole, which is far less than we can measure. This is why we can say that, for chemical reactions, mass and energy are conserved independently." http://www.chem.ox.ac.uk/vrchemistry/Conservation/page05.htm Similar figures are included on this page: The Conservation of Mass-Energy "The Law of Conservation of Mass is still a useful idea in chemistry. This is because the energy changes in a chemical reaction are so tiny that they did not affect any measurements. 100 kJ is a typical value for the energy involved in a chemical reaction and it is only about 10¯9 gram. Only recently has such a small amount been able to be accurately measured. The mass loss or gain due to energy loss or gain in a chemical reaction may someday be something that is routinely measured." http://dbhs.wvusd.k12.ca.us/Thermochem/Law-Cons-Mass-Energy.html In other words, as far as a chemist is concerned the law of conservation of mass holds true. A chemist couldn't possibly measure any difference. It's a difference that only a subatomic scientist could love (or even care about). Here's another way of putting it: Conservation Principles "If we look at mass and energy closely enough, the principles that they individually are conserved turn out to be only approximately true. Mass and energy actually are interconvertible, and are different manifestations of the same thing. We can uncouple them in thinking about chemical reactions only because the quantities of energy involved in chemical processes correspond to infinitesimal amounts of mass." http://www.chem.ox.ac.uk/vrchemistry/Conservation/page04.htm As stated above, the amount of mass lost is so tiny that it can't be measured by normal means. Early in the last century there were numerous experiments to detect such mass loss, but the amount of measured loss was always less than the amount of possible measurement area. But more recently, mass loss has been measured in certain chemical reactions. The mass loss actually turned out to be higher than expected, leading to some new theories about various types of matter. You can find out more about those experiments in the following paper: Experimental Evidence of a New Type of Quantized Matter with Quanta as Integer Multiples of the Planck Mass http://redshift.vif.com/JournalFiles/Pre2001/V06NO1PDF/V06n1vol.pdf It's all very fascinating. Like I said, I suspected the same thing as you did. The key is that the amount of mass that is lost in a typical chemical reaction is so incredibly, incredibly small that it can be assumed not to exist for all practical purposes. But it is there nevertheless. I hope this helps. Sincerely, mvguy Google search terms: "conservation of mass in chemical reactions" ://www.google.com/search?q=%22conservation+of+mass+in+chemical+reactions%22&sourceid=opera&num=25&ie=utf-8&oe=utf-8 "conservation of mass in chemical reactions" relativity ://www.google.com/search?num=25&hl=es&ie=UTF-8&oe=utf-8&q=%22conservation+of+mass+in+chemical+reactions%22+relativity&btnG=B%C3%BAsqueda+en+Google