The enthalpy of solution (or enthalpy of dissolution) is the enthalpy change associated with the dissolution of a substance in a solvent at constant pressure. In Thermodynamics and molecular chemistry, the enthalpy (denoted as H, h, or rarely as χ) is a quotient or description of A solvent is a liquid or gas that dissolves a solid liquid or gaseous Solute, resulting in a Solution.
The heat of solution is one of the three dimensions of solubility analysis. Solubility is the characteristic Physical property referring to the ability of a given substance the Solute, to dissolve in a Solvent. It is most often expressed in kJ/mol at constant temperature. The joule (written in lower case ˈdʒuːl or /ˈdʒaʊl/ (symbol J) is the SI unit of Energy measuring heat, Electricity The mole (symbol mol) is a unit of Amount of substance: it is an SI base unit, and almost the only unit to be used to measure this Just as the energy of forming a chemical bond is the difference between electron affinity and ionization energy, the heat of solution of a substance is defined as the sum of the energy absorbed, or endothermic energy (expressed in "positive" kJ/mol), and energy released, or exothermic energy (expressed in "negative" kJ/mol). A chemical bond is the physical process responsible for the attractive interactions between Atoms and Molecules and which confers stability to diatomic and polyatomic The electron affinity, E ea of an Atom or Molecule is the energy required to detach an electron from a singly charged negative The ionization potential, ionization energy or EI of an Atom or Molecule is the Energy required to remove an Electron In Thermodynamics, the word endothermic "within-heating" describes a process or reaction that absorbs Energy in the form of Heat. In Thermodynamics, the word exothermic "outside heating" describes a process or reaction that releases Energy usually in the form of Heat, but
Because heating decreases the solubility of a gas, dissolution of gases is exothermic. Consequently, as a gas continues to dissolve in a liquid solvent, temperature will decrease, while the solution continues to release energy. This is an effect of the increase in heat or of the energy required to attract solute and solvent molecules—in other words, this energy outweighs the energy required to separate solvent molecules. When the gas is "completely" dissolved (this is purely theoretical as no substance can infinitely dissolve)—the heat of solution will be at its maximum.
Dissolution can be viewed as occurring in three steps:
- Breaking solute-solute attractions (endothermic), see for instance lattice energy in salts. The lattice energy of an ionic solid is a measure of the strength of bonds in that ionic compound
- Breaking solvent-solvent attractions (endothermic), for instance that of hydrogen bonding
- Forming solvent-solute attractions (exothermic), in solvation. A hydrogen bond results from a Dipole-dipole force between an Electronegative atom and a Hydrogen atom bonded to Nitrogen, Oxygen Solvation, commonly called dissolution, is the process of attraction and association of Molecules of a Solvent with molecules or Ions of a
The value of the overall enthalpy change is sum of the individual enthalpy changes of each step. For example dissolving ammonium nitrate in water will decrease the temperature of water (solvation does not weigh up against energy spent in breaking down the crystal lattice) while adding potassium hydroxide will increase it. The Chemical compound ammonium nitrate, the Nitrate of Ammonia with the chemical formula N[[Hydrogen H]]4 N[[Oxygen O]]3 Potassium hydroxide is the Inorganic compound with the formula K[[hydroxide OH]]
Solutions with negative heats of solution form stronger bonds and have lower vapor pressure.
| Heat of solution for some selected compounds | ||
| hydrochloric acid | - | 17. Hydrochloric acid is the Solution of Hydrogen chloride ( H[[Chlorine Cl]] in water 89 |
| ammonium nitrate | + | 6. The Chemical compound ammonium nitrate, the Nitrate of Ammonia with the chemical formula N[[Hydrogen H]]4 N[[Oxygen O]]3 14 |
| ammonia | - | 7. Ammonia is a compound with the formula N[[hydrogen H3]] It is normally encountered as a Gas with a characteristic pungent Odor 29 |
| potassium hydroxide | - | 13. Potassium hydroxide is the Inorganic compound with the formula K[[hydroxide OH]] 77 |
| caesium hydroxide | - | 17. Caesium hydroxide (CsOH is a Chemical compound consisting of an atom of Caesium and a Hydroxide group (also known as Hydroxyl) 10 |
| sodium chloride | + | 3. For sodium chloride in the diet see Salt. Sodium chloride, also known as common salt, table salt, or Halite, is a 89 |
| potassium chlorate | + | 9. Potassium chlorate is a compound containing Potassium, Chlorine and Oxygen, with the chemical formula KClO3 89 |
| acetic acid | - | 0. Acetic acid, also known as ethanoic acid, is an organic chemical compound, giving Vinegar its sour taste 360 |
| Change in enthalpy ΔH | ||
See also
References
- ^ CRC Handbook of Chemistry and Physics 65th Ed. In Thermodynamics and molecular chemistry, the enthalpy (denoted as H, h, or rarely as χ) is a quotient or description of This article is about the unit of energy For its use in Nutrition and Food labelling regulations, see the article on Food energy. The mole (symbol mol) is a unit of Amount of substance: it is an SI base unit, and almost the only unit to be used to measure this In Physics, heat, symbolized by Q, is Energy transferred from one body or system to another due to a difference in Temperature In Chemistry, a solution is a Homogeneous Mixture composed of two or more substances Thermometric titration is one of a number of instrumental Titration techniques where endpoints can be located accurately and precisely without a subjective interpretation The CRC Press, LLC is a publishing group which specializes in producing technical books in a wide range of subjects
Dapyx Software network: MP3 Explorer | Ebook Manager | Zenithic