Question

2. Some ionic compounds are hydrates—solid compounds to which is bound a specific

percentage of water. Some hydrates melt when heated and release energy when they


solidify. For example, at 32 °C, liquid Glauber's salt-sodium sulfate decahydrate,


Na S04:10 H,00)—solidifies and releases 78. 0 kJ/mol of energy. Calculate the


enthalpy change when 2. 50 kg of Glauber's salt enters the solid state?

Answer 1

The enthalpy change when 2.50 kg of Glauber's salt solidifies is calculated by first converting the mass to moles using the molar mass, then multiplying by the enthalpy change per mole of 78.0 kJ/mol.

Step-by-step explanation:

The question asks to calculate the enthalpy change when 2.50 kg of Glauber's salt (sodium sulfate decahydrate, Na2SO4·10H2O) solidifies. Given that the enthalpy release of Glauber's salt during solidification is 78.0 kJ/mol, we first need to convert the mass of Glauber's salt to moles and then use the enthalpy release per mole to find the total energy change.

To convert from kilograms to moles, we use the molar mass of Glauber's salt:

• Molar mass (Na2SO4·10H2O) = (2×23.0) + (32.1) + (4×16.0) + (10×18.0) = 322.2 g/mol
• Mass of Glauber's salt = 2.50 kg = 2500 g
• Number of moles = mass (g) / molar mass (g/mol) = 2500 g / 322.2 g/mol

Now, to find the total enthalpy change, we multiply the number of moles by the enthalpy change per mole.

Total enthalpy change (kJ) = number of moles × 78.0 kJ/mol

After calculating the number of moles and multiplying by the enthalpy change per mole, you get the total energy change when 2.50 kg of Glauber's salt solidifies.