Option Explicit
Sub Abgleich()
    Dim zaehler1 As Long, zaehler2 As Long, zeile As Long, zaehler4 As Long
    Dim zaehler3 As Integer
    Dim schalter As Boolean
    Worksheets(1).Activate
    zeile = Cells(Rows.Count, 3).End(xlUp).Row * 2
    ReDim wks1(zeile, 11) As Variant
    ReDim wks2(zeile, 11) As Variant
    wks1() = Range("A1:K" & zeile)
    Worksheets(2).Activate
    wks2() = Range("A1:K" & zeile)
    For zaehler1 = 1 To zeile - 1
        For zaehler2 = 1 To zeile - 1
            If wks2(zaehler1, 3) = wks1(zaehler2, 3) Then
                schalter = True
                For zaehler3 = 1 To 11
                    If wks1(zaehler1, zaehler3) = "" Then
                        wks1(zaehler2, zaehler3) = wks2(zaehler1, zaehler3)
                    End If
                Next zaehler3
            End If
        Next zaehler2
        If schalter = False Then
            zaehler4 = zaehler4 + 1
            For zaehler3 = 1 To 11
                wks1(zeile / 2 + zaehler4, zaehler3) = wks2(zaehler1, zaehler3)
            Next zaehler3
        End If
        schalter = False
    Next zaehler1
    Worksheets(1).Activate
    Range("A1:K" & zeile) = wks1()
End Sub