# Need some help on chem questions (1 Viewer)

#### Life'sHard

##### New Member
Any help is appreciated
Answer for 1st Q is D and 1nd Q is A

#### Life'sHard

##### New Member
Why do you do 0.2-0.16/2 ?

##### Member
0.20 is the intital number of moles. When the system reaches equilibrium, 0.16 mol of PCl5 is used to produce 0.16 mol of PCl3 and Cl2. Hence, the moles left in equilibrium is 0.20-0.16 = 0.04

#### Life'sHard

##### New Member
So the 0.16 mol of chlorine includes the PCL3 and Cl2?

##### Member
ye. becoz they are the products and the molar ratios are the same.

#### Life'sHard

##### New Member
Cheers man thanks! Appreciate you.

#### CM_Tutor

##### Moderator
Moderator
The second answer is correct but the working is a touch out as "0.20 - 0.16 / 2" looks like the divided by 2 applies only to the 0.16. More clearly:

$\bg_white \cfrac{[\text{PCl}_3][\text{Cl}_2]}{[\text{PCl}_5]} = \cfrac{\frac{0.16}{2} \times \frac{0.16}{2}}{\frac{0.20 - 0.16}{2}} = \cfrac{0.08 \times 0.08}{0.02} = 4 \times 0.08 = 0.32$