In: Chemistry
Suppose we seal I2(g) and H2(g) in a vessel at T = 400 K with partial pressures PI2 = 0.067 atm and PH2= 1.275 atm. At this temperature H2 and I2 do not react readily to form HI(g), although in principle if we waited long enough they would produce HI(g) at its equilibrium partial pressure. Instead of waiting for this to happen, we choose to heat the gases in the sealed flask to 600 K, where they readily react to form HI(g). For the equilibrium
the equilibrium constant has been experimentally determined to be Keq = 38.6 at 600 K. What will PH2, PI2 and PHI be when equilibrium is established at T = 600 K?
The reaction will be
H2 + I2 --> 2HI
Pressures
Initial 1.275 0.067 0
Change -x -x 2x
Equilb 1.275-x 0.067-x 2x
Keq = 38.6 = [HI]^2 / [H2] [I2] = (2x)^2 / (1.275-x) (0.067-x)
38.6 = 4x^2 / (0.085 - 1.275 x - 0.067x +x^2
3.281 - 49.215x - 2.586x + 38.6x^2 = 4x^2
3.28 -51.50x + 34.6x^2 = 0
On calculating the equation
x = 1.42 or x = 0.067
The possible value is x = 0.067
So Partial pressure of H2 = pH2 = 1.275-0.067 = 1.208
pI2 = 0.067-0.067 = 0
pHI = 2x = 2X0.067 = 0.134