- #1
SakuRERE
- 68
- 5
Homework Statement
An ideal gas has a molar mass of 40 g and a density of 1.2 kg m-3 at 80°C. What is its pressure at that temperature?
Homework Equations
PV=nRT
R constant= 8.314
n= number of moles
T= tempreture in kelvin
density=Mass/ Volume
The Attempt at a Solution
i simply solved it like this:
i found first the volume:
V=molar mass/ density
V= 0.04kg/ 1.2kg/m^3
= 0.03 m^3
and then i just substituted in the ideal gas law
P=nRT/V (where n is the moles and here we have 1 mole)
P= (1)*(8.314)*(353K)/ (0.03) = 97828.06 Pa
but my professor solved it like this:
T = 273 + 80 = 353 K
PV = nRT
m = rV
so V = 0.04 / 1.2 with n = 1 (since 1 mole of gas has a mass of 40 g, or 0.04 kg)
P = RT/V = 8.3 x 353 x 1.2/0.04 = 8.79x104 Pa
I noticed that he didn't find the volume first and then substituted but he substituted directly in the ideal gas law! why it should be like this!?