scriem cele doua reactii:
0,2a 0,2a 0,2a
C2H6 --(>650oC)--> C2H4 + H2
1 1 1
0,8a 0,8a
C2H6 --(>650oC)--> C2H6 netransformat
1 1
---------- ---------------------------------
n moli a moli amestec gaze
=> total introdus = n moli = a
=> transformat in H2 = 0,2a
=> rand.transf. = 0,2ax100/a = 20%