heat of hydration

Examples of heat of hydration in the following topics:

• Solutions and Heats of Hydration

  • When ions dissolve in water, the stabilizing interactions that result release energy called the "heat of hydration."
  • M^+ (g) + X^-(g) \to M^+ (aq) + X^-(aq)$ [heat of hydration]
  • The heat (enthalpy) of solution (Hsolution) is the sum of the lattice and hydration energies ( Hsolution = Hhydration + Hlattice energy).
  • A hot solution results when the heat of hydration is much greater than the lattice energy of the solute.
  • Predict whether a given ionic solid will dissolve in water given the lattice energy and heat of hydration

• Elimination Reactions of Alcohols

  • This is yet another example of how leaving group stability often influences the rate of a reaction.
  • Four examples of this useful technique are shown below.
  • It should be noted that the acid-catalyzed dehydrations discussed here are the reverse of the acid-catalyzed hydration reactions of alkenes.
  • The dehydration reaction is shown by the blue arrows; the hydration reaction by magenta arrows.
  • The predominance of the non-Zaitsev product (less substituted double bond) is presumed due to steric hindrance of the methylene group hydrogens, which interferes with the approach of base at that site.

• Naming Hydrates

  • The name of a hydrate follows a set pattern: the name of the ionic compound followed by a numerical prefix and the suffix -hydrate.
  • The name of a hydrate follows a set pattern: the name of the ionic compound followed by a numerical prefix and the suffix "-hydrate."
  • The notation of hydrous compound · nH2O, where n is the number of water molecules per formula unit of the salt, is commonly used to show that a salt is hydrated.
  • An anhydride can normally lose water only with significant heating.
  • Generate the chemical formula and systematic name of a given inorganic hydrate

• Specific Heat and Heat Capacity

  • Heat capacity is a measure of the amount of heat energy required to change the temperature of a pure substance by a given amount.
  • the molar heat capacity, which is the heat capacity per mole of a pure substance.
  • How much heat is required to raise the temperature of 36 grams of water from 300 to 310 K?
  • Specific heat capacity is the measure of the heat energy required to raise the temperature of a given quantity of a substance by one kelvin.
  • Latent heat of melting describes tœhe amount of heat required to melt a solid.

• Physical and Chemical Changes to Matter

  • Many physical changes are reversible (such as heating and cooling), whereas chemical changes are often irreversible or only reversible with an additional chemical change.
  • Blending a smoothie, for example, involves two physical changes: the change in shape of each fruit and the mixing together of many different pieces of fruit.
  • The formation of gas bubbles is often the result of a chemical change (except in the case of boiling, which is a physical change).
  • When exposed to water, iron becomes a mixture of several hydrated iron oxides and hydroxides.
  • The heat from cooking an egg changes the interactions and shapes of the proteins in the egg white, thereby changing its molecular structure and converting the egg white from translucent to opaque.

• Reactions of Alkenes and Alkynes

  • Oxidation of alkynes by strong oxidizing agents such as potassium permanganate or ozone will yield a pair of carboxylic acids.
  • As the hydrogen is immobilized on the surface of the catalyst, the triple or double bonds are hydrogenated in a syn fashion; that is to say, the hydrogen atoms add to the same side of the molecule.
  • The halogenation of an alkene results in a dihalogenated alkane product, while the halogenation of an alkyne can produce a tetrahalogenated alkane.
  • Hydration of alkenes via oxymercuration produces alcohols.
  • Give examples of the various reactions that alkenes and alkynes undergo

• Reductions & Oxidations of Carboxylic Acids

  • One third of the hydride is lost as hydrogen gas, and the initial product consists of metal salts which must be hydrolyzed to generate the alcohol.
  • The resulting salt of a carbonyl hydrate then breaks down to an aldehyde that undergoes further reduction.
  • The following reactions are all examples of decarboxylation (loss of CO2).
  • The weak oxygen-halogen bond in this intermediate cleaves homolytically when heated or exposed to light, and the resulting carboxy radical decarboxylates to an alkyl or aryl radical.
  • In this respect remember the addition of hypohalous reagents to double bonds and the facile bromination of anisole.

• Cyclohexadienone Reactions

  • The photo-isomerization shown above is one example of a general family of reactions known as di-π-methane rearrangements, other examples of which are illustrated in the following diagram.
  • If the solvent is changed to 45% aqueous acetic acid a different hydrated product, isophotosantonic lactone, is formed.
  • Rationalizing the formation of isophotosantonic lactone from santonin by irradiation in aqueous acetic acid was complicated by the fact that this hydrated enone was also obtained by heating lumisantonin in the same solvent.
  • Nevertheless, the photochemical reaction is unlikely to proceed by way of lumisantonin, since heat is not required and photolysis of lumisantonin in aqueous acetic acid yields photosantonic acid rather than isophotosantonic lactone.
  • The thermal isomerization of lumisantonin in acetic acid is drawn at the bottom of the diagram.

• Heat and Work

  • When energy is exchanged between thermodynamic systems by thermal interaction, the transfer of energy is called heat.
  • The units of heat are therefore the units of energy, or joules (J).
  • For example, when heat transfers from the hot water at the bottom of the pot to the cooler water at the top of the pot.
  • Work is the transfer of energy by any process other than heat.
  • This means that the total energy within a system is affected by the sum of two possible energy transfers: heat and work.

• Crystalline Solids

  • When a pure crystalline compound is heated, or a liquid cooled, the change in sample temperature with time is roughly uniform.
  • The length of the horizontal portion depends on the size of the sample, since a quantity of heat proportional to the heat of fusion must be added (or removed) before the phase change is complete.
  • Below the temperature of the isothermal line ced, the mixture is entirely solid, consisting of a conglomerate of solid A and solid B.
  • Polymorphism is similar to, but distinct from, hydrated or solvated crystalline forms.
  • A common example of changes in polymorphism is shown by chocolate that has suffered heating and/or long storage.