1. Calculations in Chapter 10

2. Molar Enthalpy of Fusion Used when melting or freezing = ___energy ____ mol of substance Can be arranged to find any of the three Units for molar enthalpy of fusion will be kJ/mol and units for energy is kJ or J, (kilojoules or joules)

3. Example Problem The molar heat of fusion for water is 6.009 kJ/mol. How much energy is needed to convert 60.0 g of ice at 0°C to liquid water at 0°C? Rearrange the formula for energy Energy =  mol of substance

4. Have to convert the 60.0 g of ice to mol Divide by the molar mass of water 60.0 g/ 18.016 g/mol = 3.330373002 mol H 2 O (s) Energy = 6.009 kJ/mol  3.330373002 mol H 2 O (s) = 20.01221137 kJ 20.0 kJ needed to convert 60.0 g of ice at 0°C to liquid water at 0°C

5. Molar Enthalpy of Vaporization Used when boiling or condensing = energy mol of substance Can be arranged to find any of the three Boiling has energy required, condensing gives off energy

6. Example Problem How much heat is evolved when 275 g of ammonia gas condenses to a liquid at its boiling point? The molar enthalpy of vaporization for ammonia is 23.3 kJ/mol Have to convert the g of ammonia to mol of ammonia 275 g/ 17.034 g/mol = 16.14418222mol

7. Rearrange the formula for energy evolved Energy =  mol of substance Energy = 23.3 kj/mol  16.14418222mol Energy = 376.1594458 kJ Energy = 376 kJ

8. Another Problem What mass of steam is required to release 4.97 x 10 5 kJ of heat energy on condensation? The molar enthalpy of vaporization for water is 40.79 kJ/mol First rearrange to solve for mol Solve for mol Multiply by the molar mass to find grams Answer: 2.20 x 10 5 g H 2 O