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Question

For an ionic solid to melt, external energy must be applied to overcome the attractive forces holding its ions together. For example, sodium hydroxide must be heated to temperatures exceeding 318 degrees C for it to melt. Despite such a high melting point, sodium hydroxide readily dissolves and dissociates into its ions in water at room temperature.

a) What is the source of energy required to separate the ions from the solid sodium hydroxide?

b) Why does the resulting sodium hydroxide solution feel hot?

Answer 1

a). The source of the energy required to separate the ions from the solid NaOH is the lattice energy.

b). The resulting solution of NaOH feels hot because the dissolution process is exothermic in that heat is liberated when the NaOH dissolves.