Answer
$K_c = 0.10$
Work Step by Step
1. Write the equilibrium constant expression:
- The exponent of each concentration is equal to its balance coefficient.
$K_c = \frac{[Products]}{[Reactants]} = \frac{[ PCl_5 ]}{[ PCl_3 ][ Cl_2 ]}$
2. Substitute the values and calculate the constant value:
$K_c = \frac{( 12.0 )}{( 10.0 )( 9.0 )} = 0.13$
