CHM 2046C Module 7 Part II Sample Exam Answer

Part R: Enthalpy Change with Phase Changes 5 points

You put 2.50 L of water in a soup pot at 100 ^oC and the water slowly evaporates. How much heat must have been supplied to evaporate all the water from the pot. Δ H_vap of water is +40.7 kJ/mole and the density of water at 100^oC is 0.958 g/mL

See Example 13.5 page 608-9:

First calculate the number of moles of water in 2.5 Liters at 100^oC:

2.50 L (1000 mL/1 L) x (0.958 g/1 mL) x (1 mol H₂O/18.02 g H₂O) =

133 mole H₂O

Therefore the amount of energy required is:

133 mole H₂O x (40.7 kJ/mole) = 5413 kJ

Work problems #11 and #12 on page 635 for more examples

Also try Problems 35 & 36 on page 637 which are similar to previous problems in Module 7 in CHM 2045C