When 1 mol of Na2SO4 is dissolved in water, 2.9 kJ of heat is released, and when 1 mol of Na2SO4 * 10H2O

When 1 mol of Na2SO4 is dissolved in water, 2.9 kJ of heat is released, and when 1 mol of Na2SO4 * 10H2O is dissolved, 78.7 kJ of heat is absorbed. Determine the thermal effect of the formation of crystalline hydrate Na2SO4 * 10H2O from anhydrous salt.

In the reaction of formation of crystalline hydrate, let us express the amount of heat through x.

Na2SO4 + 10H2O = Na2SO4 * 10H2O Q = + X.

Let’s write down the salt dissolution reactions:
Na2SO4 * 10H2O + H2O = Na2SO4 Q = – 78.7 kJ. Endothermic reaction.

Na2SO4 + H2O = Na2SO4 Q = + 2.9 kJ. Exothermic reaction.

We get the equation and find x:
x – 78.7 = 2.9.

x = 78.7 + 2.9.

x = 81.6 kJ.