Question

In the reaction below, what volume of PCl₅(g) will be produced by the reaction of 18.9 L of chlorine gas with excess phosphorus (P₄) if all gas volumes are measured at STP?
P₄(g) + Cl₂(g) => PCl₅(g)(unbalanced)
Enter your answer with two decimal places and no units.

The answer should be 7.56, but I keep getting 6.92.

Balanced P4 + 10Cl2 ----> 4PCl5

1 atm * 18.9L = n (.0821)*(298)

0.7725*(4/10)*22.4

=6.92 , I multiplied it times 22.4 because its asking for volume and everything is in STP.

What am I doing wrong?

Answer 1

Reaction is

P₄ + 10 Cl₂$\rightarrow$ 4PCl₅

Accoding to avogadro's law at STP 1 mole of gas occupy volume 22.414 L then 18.9 L of chlorine = 18.9/22.414 = 0.8432229856 mole

According to reaction 10 mole of clorine produce 4 mole of PCl₅ then 0.8432229856 mole of chlorine produce

0.8432229856 $\times$ 4 /10 = 0.3372891942 mole of PCl₅

Accoding to avogadro's law at STP 1 mole of gas occupy volume 22.414 L then 0.3372891942 mole of PCl₅ occupy volume = 0.3372891942 $\times$ 22.414 = 7.559999 L = 7.56 L