Concepts of Potential Energy, Enthalpy, and Bond Energy Calculations
Patrick E. McMahon, Rosemary F. McMahon, Bohdan B. Khomtchouk in Survival Guide to General Chemistry, 2019
Example: Answer the questions by reading the following energy diagram. What is the forward reaction; i.e., the reaction formula equation for the forward reaction as shown in the diagram?What is the value for ΔH, the potential energy change for this forward reaction?What is the value for activation energy (activation barrier) for this forward reaction?What is the reverse reaction; i.e., the reaction formula equation for the reverse reaction as shown in the diagram?What is the value for ΔH, the potential energy change for this reverse reaction?What is the value for activation energy (activation barrier) for this reverse reaction?Which reaction is endothermic?Which set of molecules, reactants, or products represent the greater total (i.e., all bonds in the molecules) bond strengths?
ENTRIES A–Z
Philip Winn in Dictionary of Biological Psychology, 2003
Both endotherms and ectotherms use a variety of mechanisms to affect body temperature. (1) Altered heat exchange with the environment: increasing BLOOD flow (VASODILATION) of vessels near the body surface (in the SKIN) produces heat loss; VASOCONSTRICTION helps retain heat. A mechanism known as counter-current heat exchange is used by many endotherms—warmer blood in arteries travelling from the body core heats cooler blood in veins returning. In addition many animals have fur or feathers which insulate them: PILOERECTION (adjustment of the position of individual hairs) aids heat loss. (2) Evaporation: water is lost during BREATHING (either normal breathing or panting; dogs for example lose heat in this way) and by perspiration— SWEAT GLANDS in the skin allow evaporation of water which produces heat loss. (3) Behavioural responses: moving to warmer or cooler environments helps regulate temperature. SOCIAL BEHAVIOUR (for example huddling together to share and conserve heat) is also important. The construction of clothing or specialized dwellings (burrows, nests and so on) is also a behavioural adaptation to aid thermoregulation. MIGRATION, HIBERNATION and AESTIVATION are all behavioural adaptations to enable animals to deal with changed environmental temperatures. All of these processes can be used by endotherms and ectotherms. (4) In addition, endotherms have another mechanism: endogenous heat production. Muscle activity is important in this, as is SHIVERING (which is caused by neural impulses causing muscles to contract desynchronously) a response triggered by the brain's detection of lowered body temperature. NON-SHIVERING THERMOGENESIS is the production of heat by other endogenous means, principally through the action of BROWN ADIPOSE TISSUE (popularly known as BROWN FAT) and in the LIVER—some 20% of the body's heat is generated here.
Preoptic bombesin-like receptor-3 neurons heat it up
Published in Temperature, 2022
Ramón A. Piñol, Marc L. Reitman
A defining characteristic of endotherms, including mammals, is a warm, highly regulated, and stable core body temperature (Tb). Identifying the network of neurons controlling Tb is essential for understanding this fundamental physiology. The preoptic area (POA) is a brain region that receives afferent and local Tb sensory information and harbors efferent neurons of autonomic and behavioral thermoregulatory pathways [1]. These pathways contribute to thermoregulatory behavior, shivering and non-shivering thermogenesis, cutaneous vasomotion and cardiovascular responses. Researchers have identified POA neuronal populations in mice that reduce Tb when activated, regulating heat defense, torpor, and thermoregulation during sleep. A dozen such populations are marked by the expression of genes encoding enzymes, neuropeptides, and/or receptors and are predominantly glutamatergic. Future studies will need to better characterize these heterogenous neuronal populations, uncovering overlaps and defining subpopulations with more precise roles. A POA population that increases Tb when activated has been proposed and likely uses glutamatergic projections to the dorsomedial hypothalamus (DMH) [2]. We have now identified POA neurons expressing bombesin-like receptor-3 (POABRS3) as the first defined, specific population whose activation increases Tb [3]. This is driven by non-shivering thermogenesis through brown adipose tissue (BAT) activation, with concomitant increases in heart rate and blood pressure.
Mercury(II) decontamination using a newly synthesized poly(acrylonitrile-acrylic acid)/ammonium molybdophosphate composite exchanger
Published in Toxin Reviews, 2022
Adel A. El-Zahhar, Abubakr M. Idris
This research demonstrates the preparation of the polymeric composite adsorbent-exchanger P(AN-AA)/AMP and P(AN-AA) as well as characterization and application for the removal of Hg(II) from aqueous solutions. The surface characterization of both P(AN-AA)/AMP and P(AN-AA) indicates a significant improvement in surface pores, surface area thermal stability of P(AN-AA)/AMP than P(AN-AA) by the inclusion of AMP. The FTIR spectra of P(AN-AA)/AMP show characteristic peaks for ammonium molybdophosphate in the composite resin. The adsorption results illustrate that P(AN-AA)/AMP has an effective removal for Hg(II) from aqueous solutions with qmax of 221.23 mg/g. The adsorption process was found to be pH-dependent. The isothermal and kinetic studies show that the experimental results fit well with the Langmuir isotherm model and pseudo-second-order kinetic model, which reflect a favored process with the participation of strong chemical adsorption. The thermodynamic study indicates a favored endothermic adsorption process and free energy within the range of chemical adsorption. The reusability study address that the prepared resin could be regenerated and applied in repeated adsorption cycle with significant efficiency up to the third cycle with a removal percentage of more than 80%.
Physiological benefits likely underlie the systematic recruitment of thermoeffectors*
Published in Temperature, 2018
Nicole T. Vargas, Zachary J. Schlader
In most circumstances, the recruitment of thermoeffectors in endotherms is a coordinated event. Thermoeffectors that are physiologically ‘cheap’ are activated before more ‘expensive’ (i.e., resource consuming) responses are evoked. Thus, in humans, changes in skin blood flow are observed prior to the initiation of sweating in the heat (a body water consuming response) and increases in metabolism in the cold (an energy consuming response) [1]. It is likely that this is an evolutionarily conserved phenomenon, providing the benefit of regulating body temperature without the use of physiological resources. Importantly, behavior is considered to be the most powerful, diverse, and preferred thermoeffector, owing to its practically limitless possibilities. Despite near universal acknowledgement, an understanding of the control of behavioral thermoregulation in humans has been largely ignored compared to the control of its autonomic counterparts. By extension, it is unknown where thermal behavior fits within the orderly recruitment of thermoeffectors. Our recently published study aimed to fill this knowledge gap [2].
Related Knowledge Centers
- Brown Adipose Tissue
- Metabolism
- Shivering
- Uncoupler
- Seasonal Breeder
- Warm-Blooded
- Ectotherm
- Mitochondrion
- Cell
- Fat