1.1 What is Chemistry?

http://www.ck12.org Chapter 17. Thermochemistry

• Molar heats of fusion and vaporization allow calculations of energy changes involving a phase transition.


• Combinations of the above parameters can be used to calculate total energy changes for transitions that involve
  both temperature changes and changes of state.


• Heat of solution data provides information about enthalpy changes that occur when a solute dissolves in a
  solvent.

Lesson Review Questions

Reviewing Concepts

1. Define the following terms:
   a. heat of fusion
   b. heat of vaporization
   c. heat of solution


2. Indicate whether the following processes are exothermic or endothermic:
   a. melting of water
   b. conversion of liquid bromine to a gas
   c. condensation of chlorine gas
   d. conversion of sodium chloride crystals to molten (liquid) NaCl

Problems

1. Mercury melts at -39°C. How much energy is required to melt 150. grams of mercury if its molar heat of
   fusion is 2.29 kJ/mol?


2. Sulfur has a boiling point of 444.6°C. If the heat of vaporization for sulfur is 45 kJ/mol, how much heat is
   released when 42 grams of sulfur vapor is converted to liquid sulfur?


3. Calculate the total enthalpy change when 200. grams of water vapor at 120°C is converted to liquid water at
   42°C.


4. How much energy is involved in dissolving 76 grams of NaCl in water? Is this an exothermic or endothermic
   process?


5. Calculate the total energy involved in converting 50. grams of ice at -10°C to liquid water at 95°C.


6. If the heat of solution for LiBr is -49 kJ/mol, how many grams of LiBr must be dissolved in order to release
   3,500 joules of energy?

Further Reading / Supplemental Links

• Specific heat and heat capacity: http://www.iun.edu/~cpanhd/C101webnotes/matter-and-energy/specificheat.h
  tml


• Heat of solution: http://sunny.moorparkcollege.edu/~chemistry/chemistry_1B_labs/experiment_one.pdf


• Visual illustration of heats of solution: http://www.youtube.com/watch?v=o7adWQqvDUU

Points to Consider

• How do you determine the enthalpy of formation for a reaction that is not feasible to run in the laboratory?