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Внутренняя энергия

Внутренняя энергия тела — полная энергия этого тела за вычетом кинетической энергии тела как целого и потенциальной энергии тела во внешнем поле сил. Следовательно, внутренняя энергия складывается из кинетической энергии хаотического движения молекул, потенциальной энергии взаимодействия между ними и внутримолекулярной энергии.

Внутренняя энергия является однозначной функцией состояния системы. Это означает, что всякий раз, когда система оказывается в данном состоянии, её внутренняя энергия принимает присущее этому состоянию значение, независимо от предыстории системы. Следовательно, изменение внутренней энергии при переходе из одного состояния в другое будет всегда равно разности между ее значениями в конечном и начальном состояниях, независимо от пути, по которому совершался переход.

UNIT 28 Bond Energies

Before putting interatomic potentials to use, it will be helpful to get an idea of the energies of the bonds commonly encountered in molecules of biological relevance. This will give us a better view of the types of reactions and processes that can occur in the biological domain. We will be considering many cases in which molecules are subjected to one influence or another, and it is important that we develop a feeling for what might happen under a given set of circumstances. We might wish to know whether a given molecule is likely to be able to withstand certain conditions. Why is it, for example, that sitting in the sun can cause a change in the colour of the skin, whereas the same is not the case when we sit in front of a fire, even though the latter may be just as effective at giving us instant warmth?

A few calculations relevant to our own bodies will serve to illustrate the usefulness of being able to make quantitative estimates. It can readily be shown that the total energy of all the bonds in a typical adult body is about 250 times the energy we consume in a single day. Let us make the following approximations. First, we assume that the bonds which keep our bodies together are essentially of the C—C type. This is not true, of course, because there are many C—N and C—O bonds, but we will later discover that these two types of bond have rather similar energies anyway. Now there are roughly 5 x 10²² atoms per gram of tissue, and we can assume that there would be about three bonds per atom (i.e. that the degree of bonding is slightly larger than would be the case if all bonds occurred only in linear chains, with their two bonds per atom). This indicates that an adult human would comprise about 4 x 10²⁷ bonds. A typical covalent bond energy is approximately 0.6 aJ (i.e. 0.6 x 10^-18J), so the total energy of all the bonds in the body is about 2.4 x 10⁹ J or 0.6 x 10⁹ calories, which is indeed about 250 times the normal daily intake of 2400 kilocalories, in the well-fed portion of the world's population at least.

Define the following words using a dictionary

To withstand, to comprise, the daily intake, to consume, to estimate, approximation

Complete the sentences

1. Before putting interatomic potentials to use,…
2. We will be considering many cases in which…
3. We might wish to know whether…
4. It can readily be shown that…
5. First, we assume that the bonds which…
6. There are roughly 5 x 10²² atoms per gram of tissue, and…
7. This indicates that an adult human…