Question

If 5 moles of P4 reacted with 22 moles Cl2 according to the above reaction, determine:
a) How many moles PCl3 are produced a)________________

b) How many moles of P4 are left in excess after the reaction (if any) b)________________

c) How many moles of Cl2 are left in excess after the reaction (if any) c)________________

Answer 1

The chemical reaction is expressed as:

P4 + 6Cl2 = 4PCl3

a) How many moles PCl3 are produced

22 mol Cl2 ( 4 mol PCl3 /  6 mol Cl2 ) = 14.67 mol PCl3

b) How many moles of P4 are left in excess after the reaction (if any) 

5 mol - (14.67 mol PCl3 ( 1 mol P4 / 4 mol PCl3 ) )= 1.33 mol P4

c) How many moles of Cl2 are left in excess after the reaction (if any) 

There is no excess Cl2 after the reaction since it is the limiting reactant.

Answer 2

Answer :

(a) The moles of $PCl_3$ = 2.44 moles

(b) The moles of $P_4$ left = 1.34 mole

(c) There is no amount left of $Cl_2$ because it is completely consumed in the reaction.

Explanation :

The balanced chemical reaction will be,

$P_4+6Cl_2\rightarrow 4PCl_3$

First we have to calculate excess and limiting reactant.

From the balanced chemical reaction, we conclude that

As, 6 moles of $Cl_2$ react with 1 mole of $P_4$

So, 22 moles of $Cl_2$ react with $\frac{22}{6}=3.66$ moles of $P_4$

From this we conclude that, $P_4$ is an excess reagent because the given moles are greater than the required moles and $Cl_2$ is a limiting reagent and it limits the formation of product.

Now we have to calculate the moles of $PCl_3$ from the limiting reactant's moles.

As, 6 moles of $Cl_2$ react to give 4 moles of $PCl_3$

So, 3.66 moles of $Cl_2$ react to give $\frac{4}{6}\times 3.66=2.44$ moles of $PCl_3$

The moles of $PCl_3$ = 2.44 moles

The moles of $P_4$ left = 5 - 3.66 = 1.34 mole

There is no amount left of $Cl_2$ because it is completely consumed in the reaction.