## Delta S equations

Volume: $\Delta S = nR\ln \frac{V_{2}}{V_{1}}$
Temperature: $\Delta S = nC\ln \frac{T_{2}}{T_{1}}$

Katherine Grillo 1B
Posts: 69
Joined: Fri Sep 28, 2018 12:28 am

### Delta S equations

I'm confused about the different delta S equations. When does delta S equal q/t vs nRln(V2/V1) vs nCln(T2/T1)?

MaanasO 1A
Posts: 72
Joined: Fri Sep 28, 2018 12:26 am

### Re: Delta S equations

Hi Katherine!

dS = q/t when you're dealing with a reversible process. dS = nRln(Vf/Vi) when the process is isothermal. dS = nCln(Tf/Ti) when there's a change in temperature associated with the change in entropy. Your C value will change based on whether your volume (Cv) or pressure (Cp) are constant.

Hope that helps!

705192887
Posts: 77
Joined: Fri Sep 28, 2018 12:18 am

### Re: Delta S equations

MaanasO 1A wrote:Hi Katherine!

dS = q/t when you're dealing with a reversible process. dS = nRln(Vf/Vi) when the process is isothermal. dS = nCln(Tf/Ti) when there's a change in temperature associated with the change in entropy. Your C value will change based on whether your volume (Cv) or pressure (Cp) are constant.

Hope that helps!

In the last sentence you said the C value will change depending on whether volume or pressure are constant. Could you elaborate on that?

Zenita Leang 2K
Posts: 67
Joined: Fri Sep 28, 2018 12:28 am

### Re: Delta S equations

If you have a constant volume then you will use Cv which is equivalent to $\frac{3}{2}$R. If it has a constant pressure, then you will use Cp which is equivalent to $\frac{5}{2}$R. R is the constant on the constants and equations sheet.
{"found_math": true, "script_math_tex": 0, "script_math_asciimath": 0, "math_annotations": 0, "math_alttext": 0, "mathml": 0, "mathjax_tag": 0, "mathjax_inline_tex": 0, "mathjax_display_tex": 0, "mathjax_asciimath": 0, "img_math": 0, "codecogs_latex": 4, "wp_latex": 0, "mimetex.cgi": 0, "/images/math/codecogs": 0, "mathtex.cgi": 0, "katex": 0, "math-container": 0, "wp-katex-eq": 0, "align": 0, "equation": 0, "x-ck12": 0, "texerror": 0, "url": "https://lavelle.chem.ucla.edu/forum/viewtopic.php?t=42192", "fetch_time": 1610885609000000000, "content_mime_type": "text/html", "warc_filename": "crawl-data/CC-MAIN-2021-04/segments/1610703512342.19/warc/CC-MAIN-20210117112618-20210117142618-00522.warc.gz", "warc_record_offset": 430098410, "warc_record_length": 11313, "token_count": 491, "char_count": 1610, "score": 3.6875, "int_score": 4, "crawl": "CC-MAIN-2021-04", "snapshot_type": "latest", "language": "en", "language_score": 0.8604061603546143, "file_path": "/sailhome/yjruan/project/latent-lm/data/processed/finemath-4plus/finemath-4plus/train-00057-of-00064.parquet"}