Because of high value of hydration energy.
The standard enthalpy change of neutralization between hydrofluoric acid and sodium hydroxide is more negative because hydrofluoric acid is a weak acid, so it undergoes complete ionization during neutralization. This means it releases more heat compared to a strong acid. Additionally, the reaction between hydrofluoric acid and sodium hydroxide forms water and a salt, which are both strong electrolytes, leading to a more exothermic reaction.
The Hreaction is the difference between Hf, products and Hf, reactants
The standard enthalpy change of a reaction (delta H) is related to the standard enthalpy of formation (delta Hf) of the products and reactants involved in the reaction by the equation: delta H = Σ(Products delta Hf) - Σ(Reactants delta Hf). This equation relates the enthalpy change of a reaction to the enthalpies of formation of the substances involved in the reaction.
delta Hr is the enthalphy change of a reaction delta Hf is the enthalpy of formation where one mole of a substance is formed ( generally in its naturally occurring physical state) delta Hc is the enthalpy of combustion where one mole of a substance in its standard state undergoes combustion delta Hn is the enthalpy of neutralization where one mole of H+ reacts with OH- to form one mole of H2O delta Ha is the enthalpy of atomization where a molecule splits to form its neutral atomic components
The enthalpy change of a reaction (ΔHreaction) is related to the standard enthalpies of formation (ΔHf) of the molecules involved through Hess's Law. Hess's Law states that the overall enthalpy change for a reaction is the sum of the enthalpy changes for a series of reactions that add up to the overall reaction. The ΔHf values represent the enthalpy change when one mole of a compound is formed from its elements in their standard states.
The relationship between exothermic formation reactions and their enthalpy of formation values is that exothermic reactions release heat energy when the compound is formed. This results in a negative enthalpy of formation value (hf) because the reaction is giving off energy.
The heat of formation (∆Hf) of carbon disulfide (CS2) can be calculated using the standard enthalpies of formation of its constituent elements as follows: ∆Hf (CS2) = ∆Hf(C) + 2∆Hf(S) − ∆Hf(CS2). The standard enthalpies of formation for carbon (C) and sulfur (S) are known values and can be used in the calculation.
Enthalpy change of neutralisation is defined as the enthalpy change of a reaction where one mole of hydrogen ions reacts with one mole of hydroxide ions to form one mole of water under standard conditions of 1 atm, 298K (25 degree Celsius) and in the solutions containing 1 mol per dm3.
When hydrofluoric acid (HF) reacts with potassium hydroxide (KOH), they undergo a neutralization reaction to form potassium fluoride (KF) and water (H2O). The balanced chemical equation for this reaction is: 2HF + 2KOH -> 2KF + 2H2O. This reaction also releases heat due to the exothermic nature of the neutralization process.
2C(s) + 2H2(g) + 52.5 kJ -> C2H4
The enthalpy of neutralization of a strong acid against a strong base is always constant (13.7 kcal or 57 kJ mole-1). It is because in dilute solutions all strong acids and bases ionize completely and thus the heat of neutralization in such cases is actually the heat of formation of water from H+ and OH- ions, i.e., H+ + OH- ---> H2O; ΔH = -13.7 kcal
The enthalpy of formation (ΔHf) is the heat associated with the formation of one mole of a compound from its elements in their standard states. It represents the energy change when the compound is formed from its constituent elements under standard conditions.