Question

The volume of a gas is 200.0 mL at 275 K and 92.1 kPa. Find its volume at STP.

Answer 1

To solve this question we will use ideal gas equation:

`p*V=n*R*T`
Where:
p = pressure
V = volume
n = number of moles
R = gas constant
T = temperature

We can rearrange formula to get:

`(p*V)/(T) =n*R`
We are working woth same gas so we can write following formula. Index 1 stands for conditions before change and index 2 stands for conditions after change.

`( p_(1)*V_(1) )/(T_(1)) = ( p_(2)*V_(2) )/(T_(2))`

We are given:
p1=92.1kPa = 92100Pa
V1=200mL = 0.2L
T1=275K
p2= 101325Pa
T2=273K
V2=?

We start by rearranging formula for V2. After that we can insert numbers:

`{ p_(1)*V_(1) *T_(2)} = { p_(2)*V_(2)*T_(1) } \\ \\ V_(2)= (p_(1)*V_(1) *T_(2))/( p_(2)*T_(1)) \\ \\ V_(2)= (92100*0.2*273)/(101325*275) \\ \\ V_(2)= 0.18L=180mL`