Constant temperature and pressure question?

[chickenpop]

I a bit lost on a particular part of the solutions I looked up

Q. In 1L vessel, 600ml of chlorine gas is added to 400ml of ethane. Assuming constant temperature and pressure, what volume is produced of cloroethane?

A.
n(C2H6) : n(Cl2)
1 : 1
So C2H6 is the limiting reagent. <= What's the reason for this? I've racked my brains out trying to figure it out, bet it's glaringly obvious 
n(C2H6) : n(C2H5Cl)
1 : 1
As all of the species in the equation are all gases, then
V(C2H6) : V(C2H5Cl)
1 : 1
So V(C2H5Cl) = 400 mL

[Blakhitman]

Is the number of mole of C2H6 calculated less than the number of mole of Cl2?

[m@tty]

At constant temp and pressure volume is proportional to mole, so you don't need to convert to mole. As there is a required 1:1 ratio the 400mL of ethane is limiting.

[Blakhitman]

And that's why I'm gonna fail chem I never realise these things quickly, I wasted heaps of time on a question like this recently and then realised, HEY Volume ratios...and here I am making the same mistake....

[chickenpop]

so when it's same temp and pressure, we look at the volume instead of the moles to see which is limiting, and that's why 400ml is limiting right?

[Martoman]

Exactly. I imagine it always what would happen. If its same temp and pressure then the only thing that will make a difference is if you have a different amount. This is accounted for by mol as mol is just a arbitrary counting facility. And having more volume hey! well thats the same as having more mol! So that's why they are proportional.