Short answer to your question -- No, I've never seen those chips, and don't know what "CHEM" means ... but I will offer some total speculation anyway.

Fred Beck was married to Jessie Beck, though that wasn't until 1951 (3 years after these CHEM chips were made in 1948). And of course, Jessie Beck went on to own & operate Jessie Beck's Riverside casino in Reno later on. (See ChipGuide's page for her casino.) Seems that TRKing chips -- Large Crowns, then Small Crowns -- were a favorite of the Beck's.

But back to Fred Beck circa 1940's: At that time he was leasing/operating 3 concessions at Harold's Club in Reno, per the article linked below. Those 3 games were Poker, Horseracing and Keno. In addition, Fred Beck was operating Pan games at Harold's Club. See the Pan chips, from 5-cents and up, and some color-up denominations, as shown on the Harold's Club page on ChipGuide, with the "FAB" hot-stamped letters.

Here's the link to an interesting historical article on Jessie Beck, from "Nevada Magazine" --

https://nevadamagazine.com/issue/fall-2022/20471/

Now the speculation: Poker certainly uses chips, but 500 is not enough for Poker. And Horseracing and Keno don't normally use chips at all. But what if CHEM is the initials or name of someone that Fred Beck sub-leased one of his concessions to; or perhaps an assistant that helped him run the games? In essence, they could have been used as an accounting tool between Fred Beck and someone else. Or even an accounting tool between Fred Beck and Harold's Club, until they periodically "settled up".

Again, that's just speculation. But I did enjoy finding and reading that article on Jessie Beck. One of the colorful players in Northern Nevada gaming.