Oklahoma State University BCE

Last modified: Wed 12/31/1969 06:00:00 pm Oklahoma State University BCE

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Answer all of the questions below. If you do not know an answer enter CNA. However, it will help me the most if you answer each question with your best intuition/idea about what would be a reasonable answer.

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1. The enthalpy of formation, H^o_f , for an unknown compound, AB, in the solid phase and the gaseous phase were determined by experiment. The person doing the experiment forgot to associate the value of the H^o_f to the specific phase. Can you help?

The two values were; H^o_f = -23 kJ mol^-1 and -35 kJ mol^-1. Explain your reasoning.

2a. Write a balanced chemical equation showing AB converting from the solid phase to the gaseous phase.

b) Using the data in Q1 determine the H^o_rxn for the equation you wrote in Q2a.

kJ mol^-1

3. Briefly explain what the term entropy means to you.

4. Identify the phase of the substance in each of the containers labeled A, B and C. Rank order the phases in terms of the amount of dispersion in terms of position and energy the particles can occupy/have.

Container	Phase	Number of Microstates (most, next most, least)
A
B
C

5. Indicate for each change if the products are more dispersed or less dispersed compared to the reactants.

a. H₂O(l) ----> H₂O(s)

b. CO₂(s) ----> CO₂(g)

c. 2Na(s) + 2H₂O(l) ----> 2NaOH(aq) + H₂(g)

d. 2H₂(g) + O₂(g) ----> 2H₂O(g)

6. For the following four reactions the H°_rxn has been provided.

a) Predict the sign of S (the change in entropy) for each reaction a through d?

Reaction	H°_rxn	S°_rxn
a. 2H₂(g) + O₂(g) ----> 2H₂O(g)	-
b. Ba(OH)₂^.8H₂O(s) + 2NH₄SCN(s) ----> Ba(SCN)₂(aq) + 10H₂O(l) + 2NH₃(aq)	+
c. 2NO(g) + 2CO(g) ----> N₂(g) + 2CO₂(g)	-
d. C₃H₈(g) + 5O₂(g) ----> 3CO₂(g) + 4H₂O(l)	-

b) Given that the thermodynamic favorability for a reaction depends on both H°_rxn and S°_rxn answer the following questions:

a) Identify the reaction(s) (enter the letter for the reaction(s)) that you believe are most likely thermodynamically favored:

What reasoning did you use for your choice(s)

b) Identify the reaction(s) (enter the letter for the reaction(s)) that you believe are most likely not thermodynamically favored:

What reasoning did you use for your choice(s)

7. Is there anything about the questions that you feel you do not understand? List your concerns/questions.

8. If there is one question you would like to have answered in lecture, what would that question be?