Answer: Â In a perfectly isolated system, the total energy is the same.
Explanation: Â The conservation laws for mass and energy hold in a system that is isolated from its surroundings. Â The enegy released by the dissolution of solid NaOH in water is absorbed by the water. Â So the total energy of the syetm remains the same. Â It is simply converted from lattice energy of the NaOH into heat energy as measured by the temperature of the water. Â As long as it is operfectly isolated, the total energy remains the same.