Question

Hydrofluoric acid is used in the preparation of numerous pharmaceuticals (e.g., Prozac) and industrial materials (e.g., Teflon). It can be produced by the reaction of hydrogen and fluorine gases. Starting with initial concentrations of 1.69 M for H2 and 1.69 M for F2, what would be the equilibrium concentration of HF? The equilibrium constant for the reaction Kc = 115.
a. 2.85 M.
b. 4.00 M.
c. 0.85 M.
d. 3.37 M.
e. 1.69 M.

Answer 1

Answer:

the equilibrium concentration of HF is 2.85 M

Option a) 2.85 M is the correct answer.

Explanation:

Given the data in the question;

     H₂         +      F₂      ⇄     2HF

I    1.69 M        1.69 M           0

C    -x                 -x               +2x

E    1.69-x         1.69-x          +2x

given that Kc = 115        

Kc = [ HF ]² / [H₂][F₂]

we substitute

115 = [ 2x ]² / [ 1.69-x  ][ 1.69-x ]

lets find the square root of both sides

10.7238 = 2x / [ 1.69-x  ]

10.7238[ 1.69-x  ] = 2x

18.123222 - 10.7238x = 2x

2x + 10.7238x = 18.123222

12.7238x = 18.123222

x = 18.123222 / 12.7238

x = 1.424356

Hence, equilibrium concentration of HF = 2x

that is;

HF = 2 × 1.424356

HF = 2.8487 ≈ 2.85 M

Therefore, the equilibrium concentration of HF is 2.85 M

Option a) 2.85 M is the correct answer.