Assertion : Enthalpy changes are positive when Na 2 SO 4 .10 H 2 O , CuSO 4 .5 H 2 O and salt like NaCl , KCl etc. which do not form hydrates are dissolved in water. But enthalpy changes are

Question

Assertion : Enthalpy changes are positive when $Na_{2} SO_{4} .10 H_{2} O, CuSO_{4} .5 H_{2} O$ and salt like $NaCl, KCl$ etc. which do not form hydrates are dissolved in water. But enthalpy changes are negative when anhydrous salts capable of forming hydrates are dissolved in water.

Reason : The difference in the behaviour is due to large difference in the molecular weights of hydrated and anhydrous salts. The substance with larger molecular weights usually show positive enthalpy changes on dissolution.

TestHub · Accepted Answer

Enthalpy of dissolution depends on lattice energy and hydration energy, not molecular weight.

Chemistry - Thermochemistry Question with Solution | TestHub

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