The current equation uses “ΔS°<sub>f<sub>” notation, which incorrectly implies entropy of formation — a concept not typically tested or tabulated on the MCAT (enthalpy of formation is important, yes, but not entropy of formation). Instead, the MCAT uses standard absolute entropies (S°) and the equation should reflect that.
This is the version presented by Khan Academy, an accepted source, in the lesson Absolute Entropy and Entropy Change. It matches how standard entropy is calculated using values from tables, which are always in J/mol·K and given per mole. The coefficient 𝑛 accounts for stoichiometry.
(Go to 6:52 in the video)
https://www.khanacademy.org/science/ap-chemistry-beta/x2eef969c74e0d802:applications-of-thermodynamics/x2eef969c74e0d802:entropy/v/absolute-entropy-and-entropy-change
Thank you for your suggestion. I updated the card with the sum notation!