Kc Value for the Dissociation of PCl5 at 300°C

Given:
- Percentage of PCl5 not dissociated = 40% = 0.40
- Volume of the flask = 1 liter

Explanation:
1. The given information states that 40% of PCl5 is not dissociated at 300°C. This means that 60% of PCl5 is dissociated into PCl3 and Cl2.
2. Let's assume that the initial amount of PCl5 in the flask is "x" moles.
3. Therefore, the amount of PCl5 dissociated is 0.60x moles, and the amount of PCl5 not dissociated is 0.40x moles.
4. The equation for the dissociation of PCl5 is:
PCl5 ⇌ PCl3 + Cl2
5. The equilibrium constant, Kc, is defined as the ratio of the product of the molar concentrations of the products to the product of the molar concentrations of the reactants, each raised to the power of their respective stoichiometric coefficients.
Kc = ([PCl3] * [Cl2]) / [PCl5]
6. Since the initial volume of the flask is 1 liter, the molar concentrations of PCl3, Cl2, and PCl5 are equal to their respective moles.
Kc = (0.60x * 0.60x) / (0.40x)
7. Simplifying the equation, we get:
Kc = 0.36x^2 / 0.40x
Kc = 0.9x
8. As the value of x is not given, we cannot calculate the exact value of Kc. However, we can say that the value of Kc will be 0.9 times the initial amount of PCl5 in moles.

Summary:
The value of Kc for the dissociation of PCl5 at 300°C will be 0.9 times the initial amount of PCl5 in moles. The equilibrium constant, Kc, represents the ratio of the product concentrations to the reactant concentration at equilibrium.