Answer:
The reaction shifts from right to left. The new concentration of PCl₅ in equilibrium is 1.133 M.
Explanation:
The stress applied to the system is the addition of Cl₂. To offset this stress, <u>some Cl₂ reacts with PCl₃ to produce PCl₅ until a new equilibrium is established</u>.
The net reaction therefore shifts from right to left, that is,
PCl₅ (g) ← PCl₃ (g) + Cl₂ (g)
To work with the Kc expression, we need to convert the grams to moles. Since the volume of the flask is 1 liter, the moles can be expressed as molarity.
For PCl₅:
208.23 g ---------- 1 mol
3.74 g -------------- x= 1.80 x10⁻² mol ⇒ 1.80 x10⁻² M
For PCl₃:
137.33 g ---------- 1 mol
4.86 g ------------- x= 3.54 x10⁻² mol ⇒ 3.54 x10⁻² M
For Cl₂:
70.91 g ---------- 1 mol
3.59 g ----------- x= 5.06 x10⁻² mol ⇒ 5.06 x10⁻² M
Now, taking into account the shift of the equation, we make an ICE chart:
PCl₅ (g) ← PCl₃ (g) + Cl₂ (g)
i) 1.80 x10⁻² 3.54 x10⁻² 5.06 x10⁻²
c) +x -x +1.31 x10⁻² -x
e) 1.80 x10⁻² +x 3.54 x10⁻² -x 5.06 x10⁻²+1.31 x10⁻² -x
Now, we write the Kc formula:
Kc = [PCl₃] [Cl₂] / [PCl₅]
Kc = [ 3.54 x10⁻² -x] [5.06 x10⁻²+1.31 x10⁻² -x] / [1.80 x10⁻² +x]
After working with the expression, we find that x = 1.115.
Therefore, the new concentration of PCl₅ will be 1.133 M.
