College Chemistry : Non-Ideal Gas Behavior

Study concepts, example questions & explanations for College Chemistry

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Example Questions

Example Question #1 : Non Ideal Gas Behavior

One flask is at STP and another is at \(\displaystyle 100^{\circ}C\).  What is the pressure at \(\displaystyle 100^{\circ}C\)?

Possible Answers:

\(\displaystyle 0.732 atm\)

\(\displaystyle 1.37 atm\)

\(\displaystyle 1.73 atm\)

\(\displaystyle 0.841 atm\)

\(\displaystyle 1.00 atm\)

Correct answer:

\(\displaystyle 1.37 atm\)

Explanation:

The pressure of the flask at \(\displaystyle 100^{\circ}C\) is \(\displaystyle 1.37 atm\).  

\(\displaystyle \frac{P_{1}V_{1}}{n_{1}T_{1}}=\frac{P_{2}V_{2}}{n_{2}T_{2}}\)

Because the volume between the flasks and the moles in each flask are constant, we can cancel out \(\displaystyle V\) and \(\displaystyle n\).

\(\displaystyle \frac{P_{1}}{T_{1}}=\frac{P_{2}}{T_{2}}\)

At STP, conditions are \(\displaystyle 1.00 atm\) and \(\displaystyle 273.15 K\).  

\(\displaystyle \frac{1.00 atm}{273.15K}=\frac{P_{2}}{373.15K}\)

\(\displaystyle P_{2}= 1.37 atm\)

Example Question #3 : Gases

A 3.00 L container at 273 K is filled with 1.00 mol Cl2(g), which behaves non-ideally.

Using the van der Waals equation, calculate pressure exerted by the gas.

\(\displaystyle a=6.49\frac{\textrm{L}^{2}\textrm{atm}}{\textrm{mol}^{2}}\) 

\(\displaystyle b=0.0562\frac{\textrm{L}}{\textrm{mol}}\)

Possible Answers:

\(\displaystyle 3.45\textrm{ atm}\)

\(\displaystyle 7.43\textrm{ atm}\)

\(\displaystyle 7.47\textrm{ atm}\)

\(\displaystyle 6.42\textrm{ atm}\)

\(\displaystyle 6.90\textrm{ atm}\)

Correct answer:

\(\displaystyle 6.90\textrm{ atm}\)

Explanation:

Recall the van der Waals equation for non-ideal gases

\(\displaystyle \textrm{(P + }\frac{n^{2}a}{\textrm{V}})(\textrm{V - }nb)=nR\textrm{T}\)

Rewrite the equation using the known values and solve for P

\(\displaystyle [\textrm{P + }\frac{(1\textrm{ mol})^{2}(6.49\frac{\textrm{L}^{2}\textrm{ atm}}{\textrm{mol}^{2}})}{(3.00\textrm{ L})^2}][\textrm{3.00 L - (1 mol)}(0.0562\frac{\textrm{L}}{\textrm{mol}})]=(1\textrm{ mol})^{2}(0.0821\frac{\textrm{atm}}{\textrm{mol K}})(273K)\)

\(\displaystyle (\textrm{P + 0.721 atm})(2.94\textrm{ L})=22.4\textrm{ atm L}\)

\(\displaystyle \textrm{P = 6.90 atm}\)

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