Addition of alphanumeric values, such as combine two or more molecular formula in one.

ALAMMN 

You might look around to see if there is software available (maybe even an excel add-in) that can do this.

In the meantime, you could try this user defined function. To view the function you would need to go into the vba editor (Alt+F11), find the workbook in the project explorer (Ctrl+R if project explorer window is not open), expand the workbook and double click on Module1. Then, you could drag/drop the module into other workbooks. To use, you would enter =chemformula(A1,B1) where your two formulas are in A1 and B1. I attached a workbook as well.

Public Function ChemFormula(formula1 As String, formula2 As String) As Variant
     Const elemPattern As String = "([A-Z][a-z]?)(\d+)?"
     Static regEx As Object
     Dim matches As Object
     Dim elements As Object
     Dim molecules As Long
     Dim outText As String
     Dim i As Long
     Dim dicKey As Variant
     
     
     On Error GoTo ErrHandler
     
     If regEx Is Nothing Then
          Set regEx = CreateObject("vbscript.regexp")
          
          With regEx
               .Global = True: .IgnoreCase = False: .MultiLine = False: .Pattern = elemPattern
          End With
     End If
     
     
     With regEx
          If .Test(formula1 & formula2) Then
               Set matches = .Execute(formula1 & formula2)
               Set elements = CreateObject("Scripting.Dictionary")
               
               For i = 0 To matches.Count - 1
                    With matches(i)
                         
                         If Len(.SubMatches(1)) = 0 Then
                              molecules = 1
                         Else
                              molecules = CLng(.SubMatches(1))
                         End If
                         
                         
                         If elements.Exists(.SubMatches(0)) Then
                              elements(.SubMatches(0)) = elements(.SubMatches(0)) + molecules
                                   
                         Else
                              elements(.SubMatches(0)) = molecules
                         End If
                              
                    End With
               Next i
               
               For Each dicKey In elements.Keys
                    outText = outText & dicKey
                    
                    If elements(dicKey) > 1 Then
                         outText = outText & elements(dicKey)
                    End If
               Next dicKey
                              
          Else
               Err.Raise Number:=vbObjectError + 512
               
          End If
     End With
          
          
     ChemFormula = outText
          
          
ExitProc:
     Exit Function
     
ErrHandler:
     ChemFormula = CVErr(xlErrValue)
     Resume ExitProc
     
End Function