Comments re Chapter 5 Problems:

5-1

A T/F question about standard states. Remember that the standard state specifies P = 1bar but says nothing about the temperature. It might seem that (c) should be true but the full definition also requires that any gas act ideally. (Most of them do at 1 bar and 298 K.)

5-2

Another T/F question. If you do part (b), and maybe problem 5-4, before doing part (a) you will see why (a) is false.

5-4

Relationship of DrxnH to the stoichiometry and direction of the reaction. (Review of material from General Chemistry).

5-5

Definition of a formation reaction. (Review of material from General Chemistry).

5-6

Practice writing formation reactions. (Review of material from General Chemistry).

5-8

Definition of a combustion reaction. (Review of material from General Chemistry). In a combustion reaction (ie, burning in O2) all carbon is converted to CO2, all hydrogen and all oxygen are converted to H2O, and any sulfur is converted to SO2. The fate if any nitrogen present is more complicated; if you were given a problem that included nitrogen you would be told to what it should be converted.

5-15

Calculation of the difference between DrxnH and DrxnU for a standard reaction when the volume of non-gas reactants/products is neglected and then when it is considered. Please compare values of the two corrections and also the values for DrxnH and DrxnU. How important are the differences?

5-16

A simple calculation that is mostly a review of material from General Chemistry. Because of the way formation reactions are defined DrxnH for any reaction is just S(ni DfHi), where the ni are the stoichiometric coefficients of the reactants (negative values) and products (positive values). The DfHi are available in the table in the back of the textbook.

5-19

A slightly more difficult Hess's Law exercise. (Review of material from General Chemistry).

 

 

5-15

Calculation of the difference between DrxnH and DrxnU for a standard reaction when the volume of non-gas reactants/products is neglected and then when it is considered. Please compare values of the two corrections and also the values for DrxnH and DrxnU. How important are the differences?
[When doing this problem remember that T and P are constant so that DH = DU +PDV. PDV is often approximated as RTDngas, where Dngas is the net change in the number of moles of gas. This approximation is good because (1) the change in the volumes of any liquids and solids is much smaller than any change in the volume of gases, and (2) because the PDV term is usually much smaller than the DH or DU term.]

5-24

Calculation of DHo for a reaction and then correction for a temperature change.
(The DHo298 calculation is review of material from General Chemistry).
(Do only the reaction from part a of problem 5-10.)

5-30

A very short T/F question that emphasizes the limits of applicability of an equation that is easily memorized.

5-37

Calculation of DSo for a reaction and then correction for a temperature change. (The DSo298 calculation is review of material from General Chemistry).
(Do only the reaction from part a of problem 5-10.)

5-42

Calculation in two different ways of DGo298 for a reaction.
(Do only the reaction from part a of problem 5-10.)

5-43

Calculation of the DGo value for the same reaction but at a different temperature. Please do this problem by using the results from problems 24 and 37.
(Do only the reaction from part a of problem 5-10.)

5-61

Comparisons of S values. (Review of material from General Chemistry). Remember that Sgas >> Sliq > Ssol, and that S for two substances in the same phase increases with the number of atoms in the molecule (because there are more degrees of freedom).

5-62

Estimation of DHo and DSo values from information about the type of reaction. (This topic was also covered in General Chemistry). For part (3) only you will probably need to look up the DfHo298 values in the Appendix.

5-65

Question that emphasizes the types of measurements that must be made so that a new substance (e.g., C60) can be included in thermodynamic tables.


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