chem help?

Question

A 200 mL sample of oxygen gas is collected at 26 degrees celcius and a pressure of 690 torr what volume will the gas occupy at STP
I have the conversions of temp into K V into L and Pressure into Atm I need help
I believe it is set up
.2Lx.908atm/299K X.0625
I am not sure if it is set up correctly

Answer 1

you can do like above, but I'd just solve for "V" (volume), instead on "n" (moles) like he does. His way, you end up doing an extra step. So just solve the equation for V, not for n. You'll get the answer either way, but my way is simpler.

Answer 2

From the state equation of gases first find the quantity of oxygen in moles:

p*V = n*R*T, n = p*V/R*T, n = (690/760)atm*0.2L/0.082*(26+273)K,

n = 7.4x10^(-3) mol

Now 1 mole of an ideal gas occupies 22.4 L in STP so the volume of 7.4x10^(-3) mol equals:

V = n*22.4, V = 7.4x10^(-3) * 22,4 = 0.166 L (approx.) or 166 mL

Answer 3

The equation of state of an ideal gas is:
P=nRT/V
Let us check what remains constant and what changes between the two experiments:
P changes from P1=690 to P2=760 Torr.
n remains the same (the gas can't escape from the container)
R is a constant
T changes from T1=299 to T2=298 degrees Kelvin
V changes from V1=0.2 mL to V2=x mL, which is what we want to find out.
At both conditions the gas will obey the same law:
P1=nRT1/V1
P2=nRT2/V2 Lets divide one equation by the other:
P1/P2=(nRT1/V1):(nRT2/V2)=
P1/P2=(T1*V2)/(T2*V1) isolate V2:
V2=(P1*T2*V1)/(P2*T1)=
V2=(690*298*0.2)/(760*299)=0.181 L=
V2=181 mL
notice that the units that we get are correct (volume).
Also this way you don't have to transform any of your units into other units as long as you use the same units in both equation.