Heat of phase changes and dissolution Knowledge-Based Download PDF

Questions

1. 1.

   The lattice energy required to separate one mole of solid potassium chloride ($\text{KCl}$) into gaseous ions is $+715\text{ kJ/mol}$, and the combined enthalpy of hydration of the ions is $-684\text{ kJ/mol}$. What is the molar enthalpy of solution ($\Delta H_{\text{soln}}$) of potassium chloride?

   • A) $-1399\text{ kJ/mol}$
   • B) $-31\text{ kJ/mol}$
   • C) $+1399\text{ kJ/mol}$
   • D) $+31\text{ kJ/mol}$
2. 2.

   A 16.0 g sample of ammonium nitrate (NH4NO3, molar mass = 80.0 g/mol) dissolves completely in water. How much heat is absorbed from the surroundings if the molar enthalpy of solution ($\Delta H_{\text{soln}}$) is +25.7 kJ/mol?

   • A) 128 kJ
   • B) 25.7 kJ
   • C) 10.3 kJ
   • D) 5.14 kJ
3. 3.

   How much heat is released when 54.0 g of steam condenses to liquid water at its normal boiling point? (Molar mass of H2O = 18.0 g/mol, ΔHvap = 40.7 kJ/mol)

   • A) 13.6 kJ
   • B) 40.7 kJ
   • C) 122.1 kJ
   • D) 244.2 kJ
4. 4.

   How much heat is absorbed when 72.0 g of ice melts completely at 0 °C? (Molar mass of H2O = 18.0 g/mol, ΔHfus = 6.01 kJ/mol)

   • A) 1.50 kJ
   • B) 6.01 kJ
   • C) 24.0 kJ
   • D) 433 kJ
5. 5.

   When 8.00 g of solid sodium hydroxide (NaOH, molar mass 40.0 g/mol) dissolves completely in water, 8.90 kJ of heat is released. What is the molar enthalpy of solution ($\Delta H_{\text{soln}}$) for sodium hydroxide?

   • A) $-44.5\text{ kJ/mol}$
   • B) $+44.5\text{ kJ/mol}$
   • C) $-1.78\text{ kJ/mol}$
   • D) $-22.3\text{ kJ/mol}$