PChem312 f20 w13

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Monday, Nov 9, 2020

We will now highlight how to calculate entropy (ΔS) for four processes involving ideal gases:

1) Reversible Isothermal Expansion or Compression

V_iT_i --> V_fT_i

2) Constant P, V temperature change

V_iT_i --> V_iT_f

P_iT_i --> P_iT_f

3) Changes in both V and T, constant P

V_iT_i -->V _fT_f

4) Changes in both P and T, constant V

V_iT_i -->V _fT_f

Example Problem 1

(Please write out your complete solution and email to bes by next class period)

Consider a gas undergoing the following change under constant pressure (1.00 bar) conditions; calculate the change in entropy (ΔS): V_i = 10.0 L; T_i = 298 K; T_f = 398 K

Example Problem 2

(Please write out your complete solution and email to bes by next class period)

Consider a gas undergoing the following change under constant volume (10.0 L) conditions; calculate the change in entropy (ΔS): P_i = 1.00 bar; T_i = 298 K; T_f = 398 K

Wednesday, Nov 11, 2020

Review contributions to ΔS due to ΔT, ΔV, ΔP for ideal gas/closed system.

Entropy of Phase Changes...

...continuing numbering from above...

5) Solid --> Liquid phase change (fusion/melting/freezing)

- under constant pressure (ΔH)

- under constant volume (ΔU)

For processes involving solids and liquids, ΔH ~ ΔU, hence ΔS is the same for both constant P and constant V.

6) Liquid --> gas phase change (vaporization/boiling/condensation)

- under constant pressure (ΔH)

- under constant volume (ΔU)

For processes involving gases, ΔH ≠ ΔU, hence ΔS is not the same for constant P and constant V processes.

At constant P;

At constant V;

where,

and Δn is the change in moles of gas (Products - reactants; ie. increase in the number of moles of gas)

Example Problem 3

(Please write out your complete solution and email to bes by next class period)

Poly aromatic hydrocarbons (<-- wiki link here) represent and interesting set of compounds.

Calculate the entropy of fusion for 5 PAHs.

Example Problem 4

(Please write out your complete solution and email to bes by next class period)

Calculate the entropy of vaporization for methanol, ethanol, and propanol under both constant pressure and constant volume conditions...<--i probably should have asked you to only do constant P conditions.

Thursday, Nov 12, 2020

LLNL Energy Flow Diagrams website

Exam III question: In addition to having to "retrieve" some basic numerical values from these diagrams, you will be asked to write a small paragraph (~1/2 page of text) contrasting some aspect of these diagrams between two or more years. Your paragraph must contain some numerical values and the best response will contrast multiple years and include an Excel plot representing the data being discussed. You may write this in advance of the exam period, but please keep in mind that some of the introductory questions may make your pre-written paragraph less interesting.

Cutting Paper

Stepping Stairs

3D words

Folding an Xmas tree

fancy ornament

Friday, Nov 13, 2020

Entropy of Real Gases, Solids, and Liquids...

...continuing numbering from above...

6) A real gas...

Equations --> see 5.18/5.19/5.20 and the equations used in example problems 5.1--> 5.4

Example Problem 5

(Please write out your complete solution and email to bes by next class period)

Please WRITE-OUT the complete solution to example problem 5.2 in your text, CO gas expansion (V_iT_i --> V_fT_f). In this problem they are assuming ideal gas behavior, but have provided a C_V,m value to be used. Unfortunately for you/them, this C_V,m given is actually the C_P,m value shown in table 5.2; please correct this error when working this problem. (Answer = 18.5 J/K)

Example Problem 6

(Please write out your complete solution and email to bes by next class period)

Please do example problem 5.4 in your text. It is okay to use the form of the equation given in the answer as your starting point for this calculation; this problem requires you to calculate the molar volume (V_m) using the density...follow the units!