exothermic

Examples of exothermic in the following topics:

• Exothermic and Endothermic Processes

  • Endothermic reactions absorb energy from the environment, while exothermic reactions release energy to the environment.
  • In thermodynamics, these two types of reactions are classified as exothermic or endothermic, respectively.
  • Exothermic reactions are reactions or processes that release energy, usually in the form of heat or light.
  • For this reason, the change in enthalpy, $\Delta H$, for an exothermic reaction will always be negative.
  • Paul Andersen explains how heat can be absorbed in endothermic or released in exothermic reactions.

• Changes in Temperature

  • In contrast, reactions with negative enthalpies—those that release heat into their surroundings—are known as exothermic.
  • A diagram of the reaction coordinate for an exothermic reaction is shown in .
  • Exothermic reactions will be shifted toward the reactants.

• Thermochemical Equations

  • The sign of the $\Delta H$ value indicates whether or not the system is endothermic or exothermic.
  • In an exothermic system, the $\Delta H$ value is negative, so heat is given off by the reaction.

• Addition Reactions of Alkenes

  • A majority of these reactions are exothermic, due to the fact that the C-C pi-bond is relatively weak (ca. 63 kcal/mole) relative to the sigma-bonds formed to the atoms or groups of the reagent.
  • Consequently, if the bond energies of the product molecules are greater than the bond energies of the reactants, the reaction will be exothermic.
  • Note that by convention exothermic reactions have a negative heat of reaction.

• Energy Changes in Chemical Reactions

  • Exothermic reactions release heat and light into their surroundings.
  • For example, combustion reactions are usually exothermic.
  • In exothermic reactions, the products have less enthalpy than the reactants, and as a result, an exothermic reaction is said to have a negative enthalpy of reaction.

• Heat of Solution

  • Depending on the relative signs and magnitudes of each step, the overall heat of solution can be either positive or negative, and therefore either endothermic or exothermic.
  • If more energy is released in making bonds than is used in breaking bonds, the overall process is exothermic, and ∆Hsol is negative.
  • Dissolving potassium hydroxide is exothermic.
  • Solute-solvent attractive bond formation (the exothermic step in the process of solvation) is indicated by dashed lines.

• Electron Affinity

  • For any reaction that releases energy, the change in energy (ΔE) has a negative value, and the reaction is called an exothermic process.
  • Electron capture for almost all non-noble gas atoms involves the release of energy and therefore is an exothermic process.
  • Because the release of energy is always an exothermic event, these all correspond to negative values of ΔE (indicating an exothermic process).

• Hydrogenation

  • Although the overall hydrogenation reaction is exothermic, a high activation energy prevents it from taking place under normal conditions.
  • As shown in the energy diagram, the hydrogenation of alkenes is exothermic, and heat is released corresponding to the ΔE (colored green) in the diagram.
  • This reagent must be freshly generated in the reaction system, usually by oxidation of hydrazine, and the strongly exothermic reaction is favored by the elimination of nitrogen gas (a very stable compound).

• Solid Solubility and Temperature

  • This temperature dependence is sometimes referred to as retrograde or inverse solubility, and exists when a salt's dissolution is exothermic; this can be explained because, according to Le Chatelier's principle, extra heat will cause the equilibrium for an exothermic process to shift towards the reactants.

• Oxidation of Alcohols by DMSO

  • By providing an oxygen source to fix the product hydrogen as water, the endothermic dehydrogenation process may be converted to a more favorable exothermic one.
  • Due to the exothermic nature of the reaction, it is usually run at -50 ºC or lower.