有CHEM 唔明 THANKS!

a)
"With sufficient P4"=P4 is the excess reactant, then "3 moles of Cl2" will be the limiting reactant of this reaction, so Cl2 will be used to calculate the moles of PCl5.

A "10" is seen on the equation in front of Cl2, and a "4" is seen in front of PCl5, meaning the mole ratio between Cl2:PCl5=10:4=>5:2

So we can make use of the 3 moles we have, divide by 5 and times 2, that will gives you the answer (in decimal)

b)
Again, with the same technique, make use of the mole ratio between P4 and Cl2 shall solve this problem with ease. But remember to multiply the molar mass of P4 to find grams, not moles of P4 needed by the question (number found on Periodic TableX4)
mole ratio of P4:Cl2=1:10 and given number of moles of Cl2 is 1.4 moles=>mole of P4 needed X molar mass of P4= Grams of P4 needed

c)
It is almost the same problem as part (a), except this time you have to take one step further, which is find the mole of PCl5 needed first, use mole ratio and then multiply the number of moles obtained from the mole ratio with the molar mass of Cl2 (number found on Periodic Table X2)

d)
This question involves you know the concept of "Limiting Reactant" since you will have to find which one is smaller compared to the mole ratio ON THE EQUATION, NOT the ones you are given in the question.

Mole ratio between P4:Cl2=1:10-->one mole of P4 needs 10 moles of Cl2 to react

Since 3.4(<--mole of P4) X10=34 moles > 7.3 moles of Cl2 given
(or reversely, 7.3 moles (<--moles of Cl2) /10=0.73 moles <3.4 moles of P4 given)

So, Cl2 is the limiting reactant in this problem, so just repeat the steps in part (a) and you should be able to find the answer

Good Luck and wish you sucess in Chemistry :)