What causes temperature change when solid NaOH is converted into aqueous solution?
Whenever a substance goes into solution, the crystal lattice is broken and the bonds are broken. for this some energy is absorbed from water. Then the molecules/ions of the substance dissolved in water form bonds with water or hydrated. This releases energy. Now the energy absorbed in the first instance and released in the second instance are generally not equal and one of them is usually more. When the first energy is more, a cooling is produced while heat is released when the second one is more. In the case of NaOH, the released energy in the 2nd instance is more. So the solution becomes hot. When an acid and base react whether in solid state or solution, it is actually a reaction between H+ of acid and OH- of base to produce water. This reaction always releases energy.
