What Was the Initial Quantity of Hydrogen Fluoride in the Reaction Jar?

[Speedking96]

Homework Statement

Keq at a given temperature is 4

2 HF (g) <--> H2 (g) + F2 (g)

A 1 Litre jar contains 0.045 moles of fluorine at equilibrium. What was the initial quantity of hydrogen fluoride in the reaction jar?


2. The attempt at a solution

I set the initial concentration of hydrogen fluoride as x, and filled in the attached ICE table.

Afterwards:

4 = (0.045)(0.045) / (x-0.09)^2

x = 0.1125 and 0.0675

Therefore, the final answer is 0.1125 M

 

[Qube]

Work looks good. Watch your sig figs. 0.090 moles of HF gas disappears, not 0.09 moles. Final answer should also be limited to 2 significant figures. So the final answer is not 0.1125 M but rather 0.11 M. This is assuming that the 1 Liter measurement is an exact measurement (i.e. it doesn't just have one sig fig but is excluded from sig fig considerations in that it is an exact number).

 

[Borek]

Your answer is better than the question itself. It never said you started with HF only. Not that it can be solved without this assumption.