Your request for help really needs some examples of what you are trying to achieve and what source data you have.
Is your source data just two columns, one column of chemical species names and the next column a value for each chemical species, or are there several columns of data for each chemical species.
Please include the formula you are using - the formula that will include the 'replaced' data.
From what you have said it sounds as though the VLOOKUP() function will do what you want.
If the user enters a name in Cell A1, and you have a table in cells D1 to E116 with names in D1 to D116
and values to use in the formula in cells E1 to E116,
then use VLOOKUP in your formula
The value X will be multiplied by a value from Column E, based on the name entered in cell A1.
Here is VLOOKUP in the Excel help file.
(range_lookup is TRUE or FALSE. FALSE ensures that data is only returned if there is an exact match between the lookup_value (cell A1 in this example) and a value in the first column of the table_array, in this example column D).
col_index_num tells the formula which column in the table to return data from. In the example I used 2, which is column E. If you needed to return two different values for the same chemical species, the table would have to be bigger, columns D to F and then you could use =X*VLOOKUP(A1,D1:F116,2,FALSE) - Y*VLOOKUP(A1,D1:F116,3,FALSE)