If the hydration energy is greater than the lattice energy of the solute, then the enthalpy of solution is positive(exothermic), otherwise it is negative(exothermic).
Explanation:
The process of dissolving can be endothermic (temperature goes down) or exothermic (temperature goes up).
When water dissolves a substance, the water molecules attract and “bond” to the particles (molecules or ions) of the substance causing the particles to separate from each other.
The “bond” that a water molecule makes is not a covalent or ionic bond. It is a strong attraction caused by water’s polarity.
It takes energy to break the bonds between the molecules or ions of the solute.
In an ionic solution, the existence of the lattice energy and hydration energy largely determines if the solution is exothermic or endothermic.
Lattice Energy: It is a measure of the cohesive forces that bind ions.
Hydration energy: is the amount of energy released when one mole of ions undergo hydration.
Energy is released when water molecules bond to the solute molecules or ions.
If it takes more energy to separate the particles of the solute than is released when the water molecules bond to the particles, then the temperature goes down (endothermic) i.e hydration energy is greater than the lattice energy.
If it takes less energy to separate the particles of the solute than is released when the water molecules bond to the particles, then the temperature goes up (exothermic) i.e hydration energy is less than lattice energy.
Aromatic compounds undergo substitution rather than addition reactions because the aromatic structure is maintained.
Electrophilic aromatic substitution begins with attack of the electrophile on the aromatic ring to yield a delocalized intermediate called the arenium intermediate. Loss of hydrogen from this intermediate yields the final product.
