The next version of Joplin will feature support for chemical equations using mhchem for Katex.
For example this mhchem syntax will be rendered as below in Joplin:
$\ce{CO2 + C -> 2 CO}$
///BLOCK_QUOTE_END//////BLOCK_QUOTE_START///
$C_p[\ce{H2O(l)}] = \pu{75.3 J // mol K}$
///BLOCK_QUOTE_END//////BLOCK_QUOTE_START///
$\ce{Hg^2+ ->[I-] HgI2 ->[I-][Hg^{II}I4]^2-}$
