In: Chemistry
H2 (g) + I2 (g) 2 HI (g)
Kc = 25
Initial concentrations,
[H2] = [I2] = [HI] = 1.00 / 10.0 = 0.100 M
at equilibrium, [H2] = [I2] = 0.100 - x and [HI] = 0.100 + 2x
Equilibrium constant expression can be written as,
Kc = [HI]2 / [H2][I2]
Kc = ( 0.100 + 2x)2 / (0.100 - x)(0.100 - x)
25 ( 0.0100 + x2 - 0.200x) = 0.0100 + 4x2 + 0.400x
0.250 + 25x2 - 5.00x = 0.0100 + 4x2 + 0.400x
21x2 -5.4x + 0.24x = 0
it is similar to ax2 + bx +c = 0
So, on applying quadratic equation,
x = [-(-5.4)((-5.4)2 - (4*21*0.24))] / (2 *21)
x = 0.0571 M
So, at equilibrium, [HI] = 0.100 + 2(0.0572) = 0.214 M
But, number of moles = Molarity * volume = 0.214 * 10 = 2.14 mol