Heat Of Hydration Formula

Heat Of Hydration Formula

Hydration is the process by which water hardens concrete. Hydration is a chemical event in which the main constituents of cement form chemical bonds with water molecules to produce hydrates or hydration products. Aggregates are inert particles held together by cement.

The process of water exchange in the body is called hydration. Drinking water, chewing ice, eating watery meals, drinking other liquids, or ingesting orally or directly can all help. Dehydration happens when the body does not have enough water for functioning properly. Students are advised to go to the Extramarks website for learning more about the Heat Of Hydration Formula, which provides authentic information.

  • Solvent-solving interaction

The Coulombic forces that bind ions and highly polar molecules to solids are so strong that these solids can be expected to be insoluble in most solvents. The attractive interaction between ion molecules is called lattice energy and must be overcome to form a solution. Ionic solids are insoluble in most non-aqueous solvents but tend to be particularly soluble in water.

Ionic interactions with solvents have a decisive effect on solubility. The charged ions undergo ionic dipole interactions with water, overcoming the strong Coulomb attraction, which creates an aqueous solution. Water molecules are polar. This dipole arises from the electronegativity imbalance that exists in the O–H bonds within the water molecule. In addition, the two lone pairs of oxygen in water also help stabilize positively charged ions in the solution.

Hydrated Na+H2O cationic water molecules surround and stabilize cations by interacting with the partial negative charge of the oxygen terminus.

As a result, ions in an aqueous solution are always hydrated. That is, it binds rather strongly to water molecules through ionic dipole interactions. The number of water molecules contained in the primary hydration shell that completely surrounds the ion depends on the radius and charge of the ion.

  • Lattice energy

The dissolution of the ionic solid MX in water can be imagined as a sequence of two processes:

The first reaction (ionization) is always endothermic. Much work is required to decompose the ionic crystal lattice into its constituent ions. Lattice energy is defined as the energy released when one mole of ionic solid is formed from gas ions, and increases with increasing atomic charge and decreasing atomic size (radius). The higher the lattice energy value of a compound, the greater the force required to overcome the Coulomb attraction. In fact, some compounds are strictly insoluble due to high lattice energies that cannot be overcome to form solutions.

The value of the H solution depends on the amount of hydration and the H lattice energy of the solute. Conditions favourable to solution formation are usually accompanied by negative values ​​of H solution. This occurs because the hydration process exceeds the lattice energy of the solute. As is often the case with quantities that are the sum of two large terms of opposite signs, the overall dissolution process can be either endothermic or exothermic. Although H dissolution is only one of the factors governing solution formation, enthalpy is usually the most important consideration in solution formation, as it plays a role in most thermodynamic considerations.

The average time an ion spends in its hydrated shell is about 2–4 ns, which is about two orders of magnitude longer than the lifetime of a single H2O-H2O hydrogen bond. The relative strength of these two intermolecular forces is evident. Ionic dipole interactions are stronger than hydrogen bonds.

For those wondering where the term “heat of hydration” comes from, it has to do with the fact that some solutions are very exothermic when formed. A hot solution forms when the Heat Of Hydration Formula is much greater than the lattice energy of the solute. Enthalpy diagram of the dissolution process The enthalpy diagram shows the formation of an exothermic solution. Note that the H solution is lower in energy than the solute/solvent initial enthalpy. On the other hand, an endothermic process exhibits H solution as positive and energetically higher than the initial solute/solvent enthalpy.

What Is Heat Of Hydration?

The reaction between cement and water is exothermic and releases a large amount of heat. This heat release is called heat of hydration. Heat is supplied by the hydration of 1-mole particles at constant pressure. The more hydrated the particles, the more heat is released. At carbon double bonds, hydration processes occur when hydrogen and hydroxyl ions bond to the carbon. In most cases, the reactant (usually an alkene or alkyne) reacts with water to produce ethanol, isopropanol, or 2-butanol (alcohol). The general chemical reaction of hydration is given by:

RRC = CH2 + H2O/acid → RRC – CH2 – OH

In industrial applications, for example, ethanol is produced by the hydration of ethene.

CH2 = CH2 (g) + H2O(g) ⇄ CH3CH2OH (g)

Hydration Reaction

Different connections at different speeds give off different amounts of heat. The addition of retarders to cement products alters the rapid setting properties of C3A. The fineness of the cement also has a certain effect on the rate of heat generation. Ordinary cement typically produces 89-90 calories/g in 7 days and 90-100 calories/g in 28 days. Thus, the heat-producing reaction is initially rapid and slows down indefinitely.

Formula For Heat Of Hydration

The Heat Of Hydration Formula equation is characterized by how much energy is released when one mole of particles is hydrated.

Heat Of Hydration Formula = ΔH solution – ΔH lattice energy

Heat Of Hydration In Cement

When concrete is mixed with water, an exothermic reaction occurs and a large amount of heat is released. Cold temperatures can take a long time for concrete hydration to occur during the day. As the temperature rises, rapid heat generation occurs. Contains cement and water (hydrated). Next, heating effects are considered. Heat is generated by chemical reactions with water, such as the heat generated when Portland cement sets and the difference between the heat of the solution of dry cement and the heat of the solution of partially hydrated cement. The formula for determining the Heat Of Hydration Formula of cement:

H = H1 – H2 – 0.4 (th – 25.0)


H = Heat Of Hydration Formula of annealed cement, kJ/kg,

H1 = will be the heat of solution of dry cement,

H2 = will be the heat of solution for partially hydrated sample

th = final temperature of the calorimeter at the end of the measurement of the partially hydrated sample, °C.

If the Heat Of Hydration Formula is not controlled as expected, especially for large masses and designs, the heat will be difficult to escape. The Heat Of Hydration Formula can lead to very high internal temperatures in your design. This is especially noticeable during development in temperate climates, where large amounts of cement are poured quickly or when the ratio of concrete to water is very high.

If the Heat Of Hydration Formula is not overlooked during development, elongation can occur as the concrete hardens and relieves stresses and can cause serious fractures. Expansions and retractions of nouns with trailing fractions can raise difficult questions about the intrinsic sincerity of nouns.

Sample Problems

Question 1: The lattice enthalpy of sodium chloride, ΔH of NaCl is 800 kJ/mol. To make 1 M NaCl, the heat of the solution is +7.0 kJ/mol. Find the heat of hydration of Na+ and Cl-. Where the Heat Of Hydration Formula for Cl- is -500 kJ/mol. 


given that

lattice energy = 800 kJ/mol

heat of solution = 7.0 kJ/mol

Heat Of Hydration Formula  for Cl– = -500kJ/mol

Heat Of Hydration Formula = (ΔHsolution – ΔHlattice energy)

= 7 – 800

= -793

Therefore, the Heat Of Hydration Formula of Na++ Cl– = -793

Heat Of Hydration Formula for Na+ = -793 – (-500)

Therefore, Heat Of Hydration Formula for Na+ = -293

Question 2: The heat of the dry cement solution is 90 and the heat of the sample partially hydrated solution is 100. Assume that the final calorimeter temperature of the resulting sample is 110 °C. Determine the Heat Of Hydration Formula of cement.


We know the Heat Of Hydration Formula of cement

H = H1 – H2 – 0.4 (th – 25.0)

Let H1 = 90

H2 = 100

Final calorimeter temperature is 110° C,



= -44

Therefore, the Heat Of Hydration Formula of cement is -44.

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