Chemistry 9th Edition

Published by Cengage Learning
ISBN 10: 1133611095
ISBN 13: 978-1-13361-109-7

Chapter 5 - Gases - Questions - Page 234: 27


The molar volume of $N_2$ at STP is 22.42 L/mol $N_2$. This is calculated through the ideal gas law. The molar volume of He at STP is equal to the molar volume of $N_2$ at STP. The molar volume of $N_2$ is greater than 22.42 L/mol at 1.000 atm and 25.0 degrees Celsius. The molar volume of $N_2$ collected over water is less than 22.42 L/mol.

Work Step by Step

$PV=nRT\Rightarrow \frac{V}{n}=\frac{RT}{P}\Rightarrow \frac{V}{n}=\frac{273*0.08206}{1.000}=22.42 \text{ L/mol}$ Because pressure and temperature are equal, the two gases have an equal molar volume. $\frac{P}{V}=\frac{293*0.08206}{1.000}=24.04>22.42 \text{ L\mol}$ Because $N_2$ is collected over water, part of the 1.000 atm pressure is due to the evaporation of water. Therefore, the partial pressure of $N_2$ is less than 1.000 atm thereby proving the molar volume is less than 22.42 L. On the other hand, if the partial pressure of $N_2$ was 1.000 atm, then the molar volume would be 22.42 L in this scenario.
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