We are being asked to calculate the equilibrium constant, K_{c} for the given equilibrium reaction:

**H _{2}(g) + F_{2}(g) ⇌ 2 HF(g)**

**When dealing with equilibrium and K _{c}:**

• **K _{c} **→ equilibrium units are in molarity

•

$\overline{){{\mathbf{K}}}_{{\mathbf{c}}}{\mathbf{=}}\frac{\mathbf{products}}{\mathbf{reactants}}}$

▪ **only aqueous and gaseous species** are included in the equilibrium expression

▪ the **coefficient** of each compound in the reaction equation will be the **exponent **of the concentrations in the equilibrium expression

Recall molarity:

$\overline{)\mathbf{molarity}\mathbf{}\mathbf{\left(}\mathbf{M}\mathbf{\right)}\mathbf{=}\frac{\mathbf{mol}}{\mathbf{L}}}$

**Given: **

What is the value of Kc for the reaction H_{2}(g) + F_{2}(g) <=> 2HF(g) given that when 0.010 mol H_{2} and 0.050 mol F_{2} are added to a 1.00 L container, 0.0125 mol HF is present at equilibrium.

a. 3.1x10^{1}

b. 2.5x10^{2}

c. 9.5x10^{-1}

d. 7.6x10^{1}

e. 1.1