The Kc for the reaction below is 4.8 X 10 ^-10.

1/2 N2 +1/2 O2 = NO
what is the Kc for the following reaction?
2NO=N2 +O2

The second reaction is 2x the first AND it is the reverse of the first. To correct for the 2x, K becomes K2 and to correct for the reversal, it is 1/K.

1/K2 is the correct value for the second equation if K is the correct one for the first one.