chemistry a level question help

2.0dm^3 of Cl2 gas reacts with 2.0dm3 of CLF3 gas to form 6.0dm3 of a gaseous compound. the reaction has a 100% atom economy and all volumes are measured at the same temperature and pressure.
What is the molecular formula of the compound formed?
A) ClF
B)Cl2F3
C) Cl3F2
D) Cl3F3
the correct answer is A, but I'm really confused overall. I just do not get this question at all idk my mind is blank. Any help would be so appreciated, the exam board is OCR A btw.

Reply 1

UtterlyUseless69

Original post by Nat4695

You can treat volumes of gases like numbers of moles, since the volume of a gas is proportional to however many moles of gas there are.

We can be pretty safe in assuming only one product is formed and so we can call the product (?).

So we know that for every 2 mol of Cl2 that react, 2 mol of ClF3 must also react and we make 6 mol of product:

2Cl2 + 2ClF3 —> 6(?)

We can simply it down, since 2 and 6 share a common factor of 2:

Cl2 + ClF3 —> 3(?)

Counting the numbers of F and Cl on the LHS, we can see there are 3 of each. These must be split equally amongst 3 molecules of (?), so (?) is ClF