On sunny days, chemical substances can store solar energy which they release lat

Question

On sunny days, chemical substances can store solar energy which they release later on. Certain hydrated salts dissolve in water in an endothermic process when they are heated and release heat when they solidify. For example, Glauber's salt (Na_2SO_4. 10 H_2O (s) solidifies at 32 degree C and releases 78.0 kJ per mole of salt. What is the enthalpy change during the solidification of 454.0 g of Glauber's salt, which is used to supply household energy, if we consider that the molar mass of this salt includes 10 molecules of water?

Explanation / Answer

Enthalpy change = 78.0 kJ /mol

mass of glauber's salt = 454.0 g

molar mass of salt = 322.1949 g/mol.

moles of salt = 454 / 322.1949

                     = 1.409 moles

enthalpy change = 78 / 1.409

enthalpy change   = 55.4 kJ/mol

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