14) The most stable conformation of 3-bromo-2-methylpentane, viewed through the C-2—C-3 bond (i.e., C-2 in the front, C-3 in the back):
H
H
Br
H
CH3
H.
Br
Br
CH
CH2CH3
CH3
CH3
H3C
CH3
I
CH3
Br
CH2CH3
II
H
CH(CH3)2
III
CH3
H
Br
A
H
CH3
H
H
IV
CH3
CH2CH3
V
a) I
b) II
c) III
d) IV
e) V
15 TL

Kp = 929551.4

Explanation:

First of all, we state the equilibrium:

4PBr₃ (g) ⇄ P₄(g) + 6Br₂(g)

In order to determine Kp, we need the partial pressure of each gas at equilibrium. Expression for Kp is:

{(Parial Pressure P₄) . (Partial Pressure Br₂)⁶} / (Partial Pressure PBr₃)⁴

Kp = 99.2 . 97.2⁶ / 97.4⁴

Kp = 929551.4

Take account that Kp can be also calculated from Kc.

Kp = Kc (RT)^Δn where Δn is the value for (final moles - initial moles) of any gas