Final answer:
The Kc value for the reverse reaction CO (g) + Cl2 (g) ⇌ COCl2 (g) is the reciprocal of the given forward reaction, resulting in a Kc value of 5x10⁹.
Step-by-step explanation:
To find the Kc value for the reverse reaction, we need to take the reciprocal of the Kc value for the forward reaction. Given that the Kc value for the reaction COCl2 (g) ⇌ CO (g) + Cl2 (g) at 100 °C is 2x10-10, the Kc for the reverse reaction CO (g) + Cl2 (g) ⇌ COCl2 (g) would be the inverse of that value.
Therefore, the Kc value for the reverse reaction is:
Kc(reverse reaction) = 1 / (2x10-10)
Kc(reverse reaction) = 5x109