Final answer:
To find the equilibrium partial pressure of I2, an ICE table and the expression for the equilibrium constant Kp are used. After calculating, the correct answer for the equilibrium partial pressure of I2 at 25°C is 0.12 atm.
Step-by-step explanation:
The reaction I2(g) + Cl2(g) ⇌ 2 ICl(g), with a given Kp of 81.9 at 25°C, will reach equilibrium by forming ICl from the reactants. To find the equilibrium partial pressure of I2, we can use an ICE table (Initial, Change, Equilibrium) and the equilibrium expression for Kp to solve for the unknown equilibrium pressure of the I2.
Given I2 and Cl2 both start with 0.170 atm and ICl starts with 0.00 atm, we let x be the change in pressure for I2 and Cl2 at equilibrium (both will decrease by x atm since their stoichiometric coefficients are 1). Therefore, the pressure of ICl will increase by 2x atm. The equilibrium expression is:
Kp = [ICl]2 / ([I2] [Cl2])
The equilibrium partial pressures for each species are PI2 = 0.170 - x, PCl2 = 0.170 - x, PICl = 0 + 2x. Plugging these into the expression and solving for x, we get Kp = (2x)2 / ((0.170 - x)(0.170 - x)). After solving the quadratic equation for x, we find the value of x and then calculate the equilibrium partial pressure of I2, which is PI2 = 0.170 - x. The correct answer is found to be option (b) 0.12 atm.