6 Key excerpts on "Energetics"

• 

  eBook - ePub

  AP® Chemistry All Access Book + Online + Mobile

  • Kevin Reel, Derrick C. Wood, Scott A. Best(Authors)
  • 2014(Publication Date)
  • Research & Education Association

    (Publisher)

  Chapter 10 Thermochemistry Energy Thermochemistry gives consideration to the fact that energy changes occur during chemical reactions. Energy (E) is defined as the ability do work (w) on a system. From a chemistry perspective, kinetic energy comes in the form of translational, vibrational, and rotational motion of molecules, whereas potential energy arises from chemical bonds and electrostatic interactions. Energy cannot be measured directly and is monitored through changes (ΔE). First Law of Thermodynamics The first law of thermodynamics is commonly called the law of conservation of energy: “energy cannot be created or destroyed.” Energy can only be converted from one form into another during chemical reactions, and therefore the energy of the universe is constant. Energy transfers occur between the system (the reaction we are studying) and the surroundings (everything else in the universe). Heat, Temperature, and Enthalpy In the realm of thermochemistry, there are three frequently used terms that are distinctly different from one another: temperature, heat, and enthalpy. Temperature (T) is a measure of the average kinetic energy of molecules, which means that at higher temperatures molecules are moving faster. On the other hand, heat (q) measures the total kinetic energy of all of the particles in a sample. We use temperature as a means to monitor heat transfers. Heat transfers are kinetic energy transfers that go from a hotter object to a cooler object until both objects are at the same temperature. According to the first law of thermodynamics, heat lost by a hotter object is gained by a colder object. In contrast, enthalpy (H) refers to the energy released or absorbed by a chemical reaction. Unless there is pressure–volume (PΔV) work performed by the system, changes in enthalpy (ΔH) are essentially the same as the heat exchanged during a reaction

  Sign up to read

  Learn more about book
• 

  eBook - ePub

  Essential Physiological Biochemistry

  An Organ-Based Approach

  • Stephen Reed(Author)
  • 2013(Publication Date)
  • Wiley

    (Publisher)

  To the non-mathematically minded, the essentially qualitative nature of biology as compared with pure chemistry or physics is an attraction. It is a common fallacy to believe that biology is a nothing more than a descriptive subject. As outlined in Chapter 1, there are facets of metabolism which can only really be appreciated when analysed quantitatively. Fortunately, the mathematical knowledge required to understand metabolic processes is fairly straightforward and the skills we will use in this chapter are little more than those of basic arithmetic, the occasional use of logarithms and the confidence to rearrange a formula. The commonest failing is not with the computation, but a failure to take appropriate care with use of units. The most important understanding to be gained from this chapter is how to interpret the data rather than how to generate them.

  2.2 BioEnergetics: the application of thermodynamic principles to biological systems

  The study of energy changes occurring in cells is fundamental to a sound understanding of metabolism, but it is also one which students often find the most challenging. The difficulties arise due to the conceptual nature of the topic and of the terms used to describe it. Whilst it is easy to picture in one’s mind eye the basic structure of a metabolic intermediate such as glucose or cholesterol and one can easily imagine a small amount of, say, the amino acid alanine in the palm of the hand, to conjure up an image of energy is not so easy.

  By virtue of their very existence, all substances are considered to possess energy. The amount of energy will however vary from one compound to another due to the nature and number and type of atoms within a molecule and the chemical bonds which hold those atoms together. During any chemical reaction, the total energies of the individual reactants will become redistributed: some part of the total is used, for instance, to make and break chemical bonds; some of the overall energy may be ‘lost’ (transferred) to the environment. Occasionally we encounter reactions in which the total energy of the reactants is insufficient to initiate the reaction. To overcome this situation, energy usually from the hydrolysis of ATP may be used to drive the reaction forward or one of the reactants will need to be ‘activated’, often with coenzyme A, often referred to as ‘active acetate’. To continue our road traffic analogy from Chapter 1, both situations are somewhat like a vehicle taking on fuel at a filling station.

  Sign up to read

  Learn more about book
• 

  eBook - ePub

  Medical Biochemistry

  • Antonio Blanco, Gustavo Blanco(Authors)
  • 2017(Publication Date)
  • Academic Press

    (Publisher)

  energy . Chemical transformations are accompanied by energy changes. Understanding these changes is important in biochemistry since it helps to recognize how metabolic processes proceed.

  Thermodynamics is the branch of physics that deals with energy and its transformations. Its basic principles are applicable to biological processes. The fundamental principles of thermodynamics are expressed in the following two laws:

  First law of thermodynamics: The total energy of the universe remains constant (all forms of energy are exchangeable; the energy is neither created nor destroyed).

  Second law of thermodynamics: The entropy of the universe increases constantly (entropy is associated with disorder or randomness).

  Energy

  Commonly, energy is defined as the capacity to produce work. Energy exists in different modes: chemical, thermal, mechanical, electrical, and radiant, all of which can be converted into each other. Energy conversions occur frequently in biological processes. The development and growth of an organism and the continuous renewal of its structures involves a large number of chemical reactions, which are only possible if there is energy input. Similarly, maintenance of body temperature in warm-blooded animals; mechanical work in muscles, cilia, and flagella; generation of electrical impulses in the nervous system; and active transport of substances across membranes are all processes that demand energy.

  The primary source of energy for all forms of life is solar radiation. This is captured and stored as chemical energy by photosynthetic organisms and transferred to other living beings through the feeding chain of biosphere. In aerobic organisms, energy is generated mainly by oxidation of substances incorporated with the food and transferred to compounds that retain it to be used when necessary.

  Chemical energy plays an important role in biological processes. The chemical energy of a compound is represented by the movement and relative position of its atoms and particles and by bonds and attractions between its elements. When a chemical reaction occurs, frequently bonds are broken or formed and the energy content of the molecules changes. The course of a chemical reaction is ultimately determined by the energy content of the system under consideration and the energy exchange between it and the environment.

  Sign up to read

  Learn more about book
• 

  eBook - ePub

  Biomolecular Kinetics

  A Step-by-Step Guide

  • Clive R. Bagshaw(Author)
  • 2017(Publication Date)
  • CRC Press

    (Publisher)

  70 ].

  First and foremost, thermodynamics provides an essential accounting method to check that kinetic schemes are internally consistent and to ensure that a proposed mechanism does not correspond to a perpetual motion device. Thermodynamics, as such, has nothing to say about the rate of a reaction, but it does indicate whether a reaction is able to proceed in a net forward or reverse direction. Nevertheless, thermodynamic concepts are implicated in theories of absolute reaction rates (Section 3.4 ). Thermodynamics also provides the tools to quantitatively describe the interconversion between different forms of energy. Chemical energy is the most relevant form for most biochemical reactions, but other forms need consideration, for example, mechanical energy in the action of motor proteins, electrical energy in ion transport, and redox reactions or photon energy in light-driven and -emitting reactions. Energy is the capacity to do work and work is formally defined as the operation of a force, F , through a distance, x . Work, w , is not a form of energy but a mechanism of its transfer that achieves or utilizes uniform motion in the surroundings (e.g., lifting a weight or stretching a spring). This contrasts with heat, q , which achieves or utilizes random motions in the surroundings [71 ]. The total energy of a system, U, is difficult to quantify, but that which is transferred, ΔU, can be defined as

  Δ U = w     +     q

  3.1

  3.1

  Heat can be utilized to generate work using a heat engine, but this requires a heat source and heat sink to be at different temperatures, as in the Carnot cycle. Biological systems usually operate at constant temperature, and so the Carnot cycle has no direct relevance [72 ]. In living systems, energy released as heat is generally dissipated to the surroundings and lost forever. This limits the efficiency of energy transduction. In addition, biological systems generally operate at constant pressure, P, and therefore show changes in volume, ΔV , during a chemical reaction. Such expansion or contraction must be allowed for in energy balance calculations. It is for this reason that we deal with enthalpy, ΔH , rather than ΔU in our accounting exercise, because ΔH allows for the PΔV

  Sign up to read

  Learn more about book
• 

  eBook - ePub

  The Global Carbon Cycle and Climate Change

  Scaling Ecological Energetics from Organism to the Biosphere

  • David E. Reichle(Author)
  • 2019(Publication Date)
  • Elsevier

    (Publisher)

  2, thus converting radiant energy into chemical energy to support their metabolic requirements. In animal systems bioEnergetics encompasses the procurement of the chemical energy in food, the digestion of food, subsequent metabolism, and the eventual energy expenditures required for living and reproducing. BioEnergetics involves, therefore, many aspects of the organism's physiology, thermal relationships, and behavior, and becomes very complex and complicated to quantify. BioEnergetics has become a very sophisticated tool in animal husbandry, for it deals with the efficiency by which animal protein can be produced economically. By the 1960s, bioEnergetics as applied to free-living animals had bifurcated into two fields of study, one approach emphasizing behavioral biology where the animal's activity patterns were studied in relation to its energy balance with its environment, and another physiological approach dealing with the metabolism of the free-living organism. In actuality both these approaches are necessary to understand the thermodynamics of organisms in nature (Reichle et al., 1975).

  By the 1970s the growing field of ecology began to utilize bioEnergetics to understand the functioning of entire ecosystems. Thus, the study of ecological, or ecosystem, Energetics developed. Ecosystem Energetics addresses the energy balance of the entire ecosystem and all its trophic levels. It consists of the ecosystem's metabolism—its primary productivity, trophic level exchanges, turnover and decomposition of detritus, growth, and reproduction. Since biologically utilized energy is the energy stored in carbon molecules, ecosystem metabolism necessarily deals with the carbon balance of the entire ecosystem (Lindeman, 1942 ; Odum, 1957 ; Smalley, 1960; Teal, 1962 ; Macfadyen, 1964 ; Phillipson, 1966 ; Woodwell and Botkin, 1970; Reichle et al., 1973). Besides plant photosynthesis and trophic level Energetics, understanding the carbon metabolism of the entire ecosystem, above and below ground, includes death and decomposition to complete the ecosystem's carbon balance (net ecosystem production) with the environment. This academically intriguing subject suddenly took on tremendous societal relevance beginning in the 1980s, with the growing concern over the combustion of fossil fuels and the resulting CO2

  Sign up to read

  Learn more about book
• 

  eBook - ePub

  Foundations for Teaching Chemistry

  Chemical Knowledge for Teaching

  • Keith S. Taber(Author)
  • 2019(Publication Date)
  • Routledge

    (Publisher)

  Here there is a spontaneous process which apparently absorbs energy (that is, the cooled mixture slowly returns to room temperature as it is heated by its surroundings), suggesting that, overall, the bonding in the solution is not as strong as that present before. The energy released as solvation occurs does not compensate for the energy needed to break bonds (e.g., between ions in the salt). Yet the process is still energetically favourable (the total free energy decreases) as the total number of ways that the energy quanta in the system can be distributed across the species in the mixture is far greater than the number of options in the separate solid and liquid before dissolving.

  That is, the increase in entropy (ΔS) (T) is sufficient to give an overall negative free energy change (ΔG) at that temperature despite an increase in enthalpy (heat entering the system, ΔH) as ΔG = ΔH – TΔS. Students at the highest levels of school chemistry sometimes have to study some basic thermodynamics and so appreciate the nature and significance of entropy to the overall free energy changes in various processes. It is probably sensible to ignore entropy in introductory teaching, and this will be less problematic when students appreciate that chemistry is understood in terms of models, which involve simplifications and so will sometimes fail to explain all examples or details of a phenomena (see Chapter 3 ).

  Chemical reactions

  Chemistry is the science that studies the properties of different substances and, in particular, their chemical properties: which substances react with which other substances, under what conditions, and what new substances are produced. Like many central ideas in chemistry, chemical reactions are understood at two levels of description (see Chapter 4 ). The actual phenomena concern changes seen in the laboratory: when a flame is applied to a balloon filled with hydrogen there is an explosion; when some magnesium ribbon is added to some hydrochloric acid solution, there is fizzing, and metal seems to incrementally disappear; when lead (II) nitrate solution is added to potassium iodide solution, a strong yellow colouration appears, the mixture becomes opaque, and over time a yellow powder settles beneath a clear liquid (see Figure 11.1

  Sign up to read

  Learn more about book