Question

A chemical system within a sealed 4.5 L reaction vessel is described by the following reversible reaction equation:
H2(g) + F2(g) ↔ 2 HF(g) (K = 30.0, at 1500 K)
1)What does the size of the equilibrium constant indicate regarding the extent of the forward reaction?
2)If some hydrogen gas and fluorine gas is added to an empty reaction vessel, determine the reaction quotient (the value of Q) initially.
3) Determine the equilibrium concentration of hydrogen fluoride gas, if 0.070 mol of hydrogen gas and 0.10 mol fluorine gas are initially placed in the 4.5 L vessel.

Answer 1

Ans: H₂(g) + F₂(g) ↔ 2 HF(g)

1) The value of K=30. we know K = K_f/k_b.

Thus the size of K indicates that the forward reaction has proceeded to 30 times more extent than the backward reaction.

2) Q = [HF]²/[H₂].[F₂]

initially [HF] = 0, as no HF has been prepared at the starting point.

Thus the reaction quotient Q initially is zero.

3) we know K = [HF]²/[H₂].[F₂]  

H₂(g) + F₂(g) ↔ 2 HF(g)

initial mole: 0.07 0.1 0

equilibrium mole: 0.07-x/2 0.1-x/2    x

Then 30 = x² /  (0.07-x/2).( 0.1-x/2) solving this we get x=0.12

then conc. of HF= n/V = 0.12mol/4.5L = 0.0267M

Thus the equillibrium concentration of HF is 0.0267M.