Question

A sample of gas occupies a volume of 4.5 L at 20 Celsius. What volume will it occupy at -15 celsius, if the pressure remains constant?
Please show your work

Answer 1

Answer: 3.96L

Explanation:

PV = nRT

The way I like to do it, it's I get rid of whatever I do not need.

We have to do an equation for sure to make both sides equal and find our desired result.

The pressure is constant, so it would be constant in both sides, therefore, there is no point in using it.

The R is a constant used in both sides so there is no point on using it either.

We don't need to work with moles in this case, so let's forget about the moles.

Therefore we are left with only V (volume ) and T(Temperature)

Which would logically make this:

V1/T1 = V2/T2

OR

T1/V1 = T2/V2

Both of these would work, we always use whatever makes our calculations easier without complicating our lives with the algebra.

That should remind you of Charles' Law

Transform degrees into kelvins

20 + 273.15 = 293.15K

-15 + 273.15 = 258.15K

So, 4.5L/293.15K = V2/258.15K

V2 = (4.5L/293.15K) x 258.15K

V2 = 3.96L