Difference between revisions of "PChem312 f20 w13"
| Line 47: | Line 47: | ||
:5) Solid --> Liquid phase change (fusion/melting/freezing) | :5) Solid --> Liquid phase change (fusion/melting/freezing) | ||
| − | ::- under constant pressure ( | + | ::- under constant pressure (ΔH) |
| − | ::- under constant volume ( | + | ::- under constant volume (ΔU) |
:::''For processes involving solids and liquids, ΔH ~ ΔU, hence ΔS is the same for both constant P and constant V.'' | :::''For processes involving solids and liquids, ΔH ~ ΔU, hence ΔS is the same for both constant P and constant V.'' | ||
| Line 54: | Line 54: | ||
:6) Liquid --> gas phase change (vaporization/boiling/condensation) | :6) Liquid --> gas phase change (vaporization/boiling/condensation) | ||
| − | ::- under constant pressure | + | ::- under constant pressure (ΔH) |
| − | ::- under constant volume | + | ::- under constant volume (ΔU) |
| + | :::''For processes involving gases, ΔH ≠ ΔU, hence ΔS is not the same for constant P and constant V processes.'' | ||
| + | |||
| + | [[File:Screen Shot 2020-11-13 at 7.58.25 AM.png|175px]], at constant P. | ||
| + | |||
| + | |||
====Example Problem 3==== | ====Example Problem 3==== | ||
Revision as of 14:02, 13 November 2020
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
- ViTi --> VfTi
- 2) Constant P, V temperature change
- ViTi --> ViTf
- PiTi --> PiTf
- 3) Changes in both V and T, constant P
- ViTi -->V fTf
- 4) Changes in both P and T, constant V
- ViTi -->V fTf
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): Vi = 10.0 L; Ti = 298 K; Tf = 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): Pi = 1.00 bar; Ti = 298 K; Tf = 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.
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.
Thursday, Nov 12, 2020
LLNL Energy Flow Diagrams website
Cutting Paper