Using the result derived in full that:
$a = (27R^2T_c^2)/(64P_c)$
$b = (RT_c)/(8P_c)$
and the van der Waals equation of state:
$P = (RT)/(barV - b) - a/(barV^2)$ ,
First, I'd convert
$P_c = "4947.6 kPa" xx "0.01 bar"/"1 kPa" = "49.476 bar"$
(compared to$"49 bar"$ from the )
$T_c = 32.1^@ "C" = "305.25 K"$
Then:
$color(blue)(a) = ((27)("0.083145 L"cdot"bar/mol"cdot"K")^2("305.25 K")^2)/(64("49.476 bar"))$
$=$ $color(blue)("5.493 L"^2cdot"bar/mol"^2)$
(compared to$"5.570 L"^2cdot"bar/mol"^2$ from .)
The
$color(blue)(b) = (("0.083145 L"cdot"bar/mol"cdot"K")("305.25 K"))/(8("49.476 bar"))$
$=$ $color(blue)("0.06412 L/mol")$
(compared to$"0.06499 L/mol"$ .)
Using this information, we can find the pressure of
$"5 g ethane" xx "1 mol ethane"/"30.0694 g" = "0.1663 mols"$
giving us a molar volume of (exactly):
$barV = "1 L"/"0.1663 mols" = "6.01388 L/mol"$
Finally, we can solve for the pressure to get:
$color(blue)(P) = (("0.083145 L"cdot"bar/mol"cdot"K")("288.15 K"))/("6.01388 L/mol" - "0.06412 L/mol") - ("5.493 L"^2cdot"bar/mol"^2)/("6.01388 L/mol")^2$
$=$ $color(blue)("3.875 bar")$
Using the , we can check our answer:
$P = (nRT)/V = (RT)/(barV) = (("0.083145 L"cdot"bar/mol"cdot"K")("288.15 K"))/("6.01388 L/mol")$
$=$ $"3.984 bar"$
which is indeed close! The real gas actually takes up less volume (its attractive forces dominate), meaning that there is more empty space in the container than we expected, and thus, a slightly smaller pressure is exerted.
Note: some textbooks ask you to go through and derive