At STP, 1.0 L Br2 reacts completely with 3.0 L F2, producing 2.0 L of a product. What is the formula?

Question

At STP, 1.0 L Br2 reacts completely with 3.0 L F2, producing 2.0 L of a product. What is the formula of the product? Assume all substances are gases.

Answer 1

The answer is BrF3.

and the balance equation is

Br2 + 3F2 ---> 2BrF3

how? get the moles of each using this formula:
n = PV/RT

you'll get:
mol Br2 = 0.041mol
mol F2 = 0.123 mol
mol pdt = 0.082 mol

base from this, you'll found that ratio of Br:F is 1:3. Hence, the product is BrF3. you'll also found that ratio of Br2:F2:pdt is 1:3:2 which also agrees with our balance equation above.

Answer 2

At 1 atm bromine won't react with fluorine, you need substantially more than atmospheric pressure to get those to react.

However, if we ignore the laws of chemistry, we could assume that 2L of product is one litre of our product, and one litre of left over fluorine. So that means that our 1 L of bromine reacted with 2 L of fluorine. Lets assume ideal gasses just for fun, so we have a stoichiometric ratio of 1:2. Thusly, our empirical formula will be BrF2. Of course, we don't know that this is the actual formula, it could be Br100F200, for all we know, except that would be too heavy to be a gas, but we've already ignored 2 fundamental laws of chemistry, so another one won't hurt....

Please ask your teacher to give you more realistic examples. In the real world when you react bromine with fluorine, you get BrF, not BrF2, or Br2F4 or whatever.