Energy in the Real World

petroleum, natural gas, and woody plants provide us with a vast resource of energy, all of which is derived from the sun. Plants use the process of photosynthesis to store the sun s energy, and we harvest that energy by burning the plants or using the decay products of the plants. These decay products have been converted over millions of years to fossil fuels. As the plants died and decayed, natural processes changed them into petroleum deposits that we now use in the forms of gasoline and natural gas. 

Although we do not really understand completely how petroleum deposits were formed, they most likely came from the remains of marine organisms living over 500 million years ago. Petroleum is composed of hydrocarbon compounds (which contain only carbon and hydrogen). Carbon is a unique element in that it can produce chains of atoms in a molecule of different lengths. Table 4.4 gives the names and formulas of some simple hydrocarbons. Natural gas is associated with petroleum deposits and consists mainly of methane with some ethane, propane, and butane mixed in. 

Alternative energy sources include wind, solar, and biofuels. 

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A change in any thermodynamic state function is independent of the path used to accomplish that change. This feature of state functions tells us that the energy change in a chemical reaction is independent of the manner in which the reaction takes place. In the real world, chemical reactions often follow very complicated paths. Even a relatively simple overall reaction such as the combustion of CH4 and O2 can be very complicated at the... 

Due to the concept of low energy, intrinsically safe electrical circuits do not provide the energy necessary to drive motors or high powered electrical equipment. Nevertheless, this does not limit or restrict their application in the real world. 

In the real world there are three directions x, y, and z. Thus, three force balances can be written for any system. Therefore, each system has three equations of motion (plus one total mass balance, one energy equation, and NC — 1 component balances). 

The energy with which electrons are bound in conducting materials is known as the electron affinity of the material. Materials with a high electron affinity bind electrons strongly and exhibit noble behavior (i.e., are relatively inert and do not oxidize spontaneously in air). Gold is an example. On the other hand, metals such as aluminum or copper are less noble and their surfaces, once exposed to air, are readily oxidized. When two dissimilar electronic conductors are placed in contact with each other, electrons flow from the material that is less noble (e.g., copper) to the more noble material (e.g., palladium) until an equilibrium is reached and the contact potential is formed at their junction. Because of the multitude of possible combinations of conductors in the real world, contact potential is the most ubiquitous of all junction potentials. 

It can easily be seen that adding function P4(r, t) to any solution of the problem defined by (13.155) and (13.156) provides another solution of the same problem. Thus, it becomes clear that there exists a set of different mathematical solutions of (13.155) and (13.156). In other words, we cannot uniquely define the real physical process by assigning the sources of oscillations and the condition of field decay at infinity. At the same time, in the real world there is only one physical solution of this problem. It becomes clear now that we should impose an additional constraint to obtain a unique, physically meaningful, solution. This constraint should be able to reject convergent waves, acquiring and carrying energy firom infinity, which is physically impossible. 

Heat capacity is always positive on the MCAT the temperature will always increase when energy is added to a substance at constant volume or pressure. In the real world, heat capacity also changes with temperature tire amount of energy that a substance can absorb per change in temperature varies with the temperature. However, unless otherwise indicated, for the MCAT, assume that heat capacity does not change with temperature. 

In the real world, the transition or equilibrium point between two enantiotropic polymorphs is often not directly observed because of suspended transformations in connection with metastable equilibrium. Measurement of various physical properties at different temperatures can be related to the relative free energy of the polymorphs, and the forms, can be classified as enantiotropic or monotropic. 

Dlott D. D. (1990), Ultrafast vibrational-energy transfer in the real world—laser ablation, energetic solids, and hemeproteins , /. Opt. Soc. B 7, 1638-1652. 

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