The Interconversion of Mass and Energy

Ionizing radiation has been used to control harmful insects. Captured males are sterilized by radiation and released to mate, thereby reducing the number of offspring. This method has been used to control the Mediterranean fruit fly in California and disease-causing insects, such as the tsetse fly and malarial mosquito, in other parts of the world. 

Radioisotopic tracers emit nonionizing radiation and have been used to study reaction mechanisms, material flow, elemental composition, and medical conditions. Ionizing radiation has been used to destroy cancerous tissue, kill organisms that spoil food, and control insect populations. 

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Mass Difference in Chemicai Reactions The interconversion of mass and energy is not important for chemical reactions because the energy changes involved in breaking or forming chemical bonds are so small that the mass changes are negligible. For example, when 1 mol of water breaks up into its atoms, heat is absorbed and we have ... 

Einstein showed that it is mass-energy that is conserved one can he converted into the other. This equivalence becomes important in nuclear reactions, discussed in Chapter 19. In ordinary chemical reactions, however, the interconversion of mass and energy is not a significant factor, and we can regard mass and energy as Independently conserved. 

The theories that have been developed to describe mass transfer arise from the law of conservation of mass, which states that mass can be neither created nor destroyed. According to this law, the total mass in a particular region in space can increase only by the addition of mass from the surroundings and can decrease only by the loss of mass back to them. Processes such as radioisotope decay and nuclear fission are exceptions to this law, since they involve the interconversion of matter and energy. In the absence of nuclear decay, however, the law of conservation of mass holds and is broadly applicable to mass transfer problems. 

Thermal pollution. The heating of the environment to temperatures that are harmful to its living inhabitants. (12.4) Thermochemical equation. An equation that shows both the mass and enthalpy relations. (6.3) Thermochemistry. The study of heat changes in chemical reactions. (6.2) Thermodynamics. The scientific study of the interconversion of heat and other forms of energy. (6.7)... 

To retain this result it is foimd that one must make a radical new assumption and introduce the relation E = mc, where mc is what is called the proper energy. The relation imphes an equivalence of mass and energy and suggests at least the formal possibility of their interconversion, since in virtue of its existence a mass has energy as it were stored up in it. 

The interconversion of butadiene radical cations and ionized cyclobutene represents a model case for a formal pericyclic process. Much work has been invested to study not only the distinguishability of these isomers and their derivatives by mass spectrometry, but also to check the role of orbital symmetry in the ionic species. Hass has addressed the latter problem in depth in a review on pericyclic reactions in radical cations in both the gas and condensed phases and no further survey on the papers mentioned there will be given here. The topic pertains also to the ring-opening of ionized benzocyclobutene to ionized ortho-quinodimethane (cf Section V) and various otha- phenyl-, methyl- and carboxy-substituted derivatives. In this context, we restrict ourselves hwe mentioning that an upper limit of 7 kcalmol only has been detemined by CE mass spectrometry for the activation barrier of the cycloreversion of the parent cyclobutene radical cations. The energy requirement for the cycloreversion of ionized 1- and 3-substituted cyclobutenes were found, by experiment, to be markedly different. Obviously, dissociation of the (in a sense bis-allylic) strained C—C bond is much more facile when the substituent is at C-3,... 

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