In: Chemistry
At a particular temperature the equilibrium constant for the reaction: H2(g) + F2(g) ⇔ 2HF(g) is K = 81.0. A reaction mixture in a 10.00-L flask contains 0.25 moles each of hydrogen and fluorine gases plus 0.37 moles of HF. What will be the concentration of H2 when this mixture reaches equilibrium?
molarity of H2 = 0.25 / 10 = 0.025 M
molarity of F2 = 0.37 / 10 = 0.037 M
H2 + F2 <-------------------------> 2HF
0.025 0.037 0 ---------------------> initial
0.025-x 0.037-x 2x ------------------------> equilibrium
K = (2x)^2 / (0.025-x) (0.037-x)
81.0 = (2x)^2 / (0.025-x) (0.037-x)
81.0 = 4x^2 / (0.025-x) (0.037-x)
x =0.023
H2 concentration at equilibrium = 0.025-x = 0.025- 0.023
H2 concentration at equilibrium = 0.002 M