CHEM 361
Assignment 27 - (OUT OF 30 PTS)
Please complete this assignment before the next class meeting. Written answers to
questions must be handed in at the beginning of class.
I. Read sections 3.1 and 3.2 in the textbook.
II. Answer the following questions. You are asked to consider the questions
below in preparation to class discussion. Any questions you have about this
homework assignment can be directed to me or your classmates.
The answers to most of these questions will be clear after you read the sections in
the textbook specified in part I. You are encouraged to discuss this assignment
with me and your classmates. However, the answers you hand in must be your
own work.
1. Which thermodynamic property is most relevant to the study of
thermochemistry? Why?
2. Distinguish between an endothermic and an exothermic process.
3. Define the terms standard state and standard enthalpy change.
4. For each of the following, give the appropriate chemical equation and standard
enthalpy value (the thermochemical equation).
Give the physical state for all reactants and products in the chemical reaction.
Use the appropriate, complete symbol for the enthalpy change, including units.
a. the standard enthalpy of vaporization for Ar at 87 K.
b. the standard enthalpy of fusion for He at 3.5 K.
c. the standard enthalpy of sublimation for C6H6.
d. the standard enthalpy of condensation (gas to liquid) for H2O at 373K.
e. the standard bond dissociation enthalpy for H2 at 298K.
f. the C-C mean bond dissociation enthalpy in C2H6 at 298K.
g. the C=C mean bond dissociation enthalpy in C2H2 at 298K.
h. the standard enthalpy of atomization of gaseous HF.
i. the standard enthalpy of combustion of liquid methanol.
5. Consider the Ei1 and Ei2 values for Na and Mg given in Table 3.2 in the
textbook. Why is Ei2/Ei1 so much larger for Na (≈ 9) than for Mg (≈ 2)?
6. Why is Eeg for Cl negative but Eeg for Ca is positive?