def _get_elmt_amt_in_rxn(self, rxn: Reaction) -> int: """ Computes total number of atoms in a reaction formula for elements not in external reservoir. This method is used in the calculation of reaction energy per mol of reaction formula. Args: rxn: a Reaction object. Returns: Total number of atoms for non_reservoir elements. """ return sum(rxn.get_el_amount(e) for e in self.pd.elements)