Question

What is the volume occupied by `3.0*10^23` molecules of bromine gas at STP?

Answer 1

`color(magenta)("11 L")`

Explanation:

`color(orange)("Because we are at STP, we will have to use the ideal gas law:")`

At standard temperature and pressure, the temperature is 273K and the pressure is 1 atm.

Next, list your known and unknown variables. Our only unknown is the volume of `Br_2(g)`. Our known variables are P,R, and T.

We don't necessarily have `n` yet, but we're given a value that will lead us to the number of moles of bromine gas. All we have to do is convert molecules to moles using the conversion factor below:

We'll use the second conversion factor because we can cancel out molecules and end up with moles:

`3.0xx10^(23)cancel"molecules"xx(1mol)/(6.02x10^(23)cancel"molecules")` `=` `0.498 mol`

Now all of the variables have good units! All that's left to do is rearrange the equation and solve for V like so:

`V = (nxxRxxT)/P`
`V = (0.498cancel"mol"xx0.0821(Lxxcancel"atm")/(cancel"mol"xxcancel"K")xx(273cancelK))/(1cancel"atm")`
`V = 11 L`