A student noticed that the size of the hot pack becomes bigger when magnesium sulfate reacts with water. She thinks that more atoms are produced that make the hot pack grow bigger. Do you agree? Explain.

Disagree with the suggestion based on the hygroscopic nature of anhydrous magnesium sulfate

Explanation:

Magnesium sulfate in the anhydrous form is a drying agent. A drying agent salts of inorganic compounds that has the capability of absorbing water to become hydrated, when placed in the presence of a wet surface or moist air

Anhydrous magnesium sulfate is therefore hygroscopic such that it absorbs water from the atmosphere and becomes hydrated and increases in size as its volume is increased according to the following chemical equation

MgSO₄(s) + 7H₂O(l) → MgSO₄·7H₂O(s)

The molar mass of anhydrous magnesium sulfate = 120.366 g/mol

The molar mass of the heptahydrate = 246.47 g/mol

Therefore, the mass of the magnesium sulfate doubles when it forms the heptahydrate, and the magnesium sulfate grows bigger.