Deviations from the Ideal Gas Law

Page 1:

  • The Ideal Gas Law (PV = nRT) is a powerful tool for predicting gas properties.

  • It can calculate the pressure, volume, number of moles, or temperature of a gas.

  • However, it is based on ideal gases and may not accurately predict values for real gases.

  • Factors that determine how well the Ideal Gas Law can predict values for real gases are being discussed.

Page 2:

  • Model 1 shows the relationships between pressure and volume for different gases.

  • The four gases illustrated in Model 1 are Helium, Neon, Argon, and Krypton.

  • Krypton has the largest deviations from the predicted pressure.

  • The actual pressures of the four gases deviate differently from the predicted values.

  • The deviations from the predicted pressure are not always in the same direction for all gases.

  • The deviations from the predicted pressure are greater at lower volumes.

  • The assumptions about molecular behavior in the Ideal Gas Law are not fully applicable to real gases.

Page 3:

  • Model 2 focuses on the volume of gas molecules and the usable space in containers.

  • The assumptions of the Ideal Gas Law state that gas atoms have no volume.

  • In reality, gas atoms do take up space, affecting the usable space in a container.

  • The "real" usable space and the percent of "ideal" space available for atom motion are calculated.

Page 4:

  • The "real" usable space and the percent of "ideal" space available for atom motion are further calculated.

  • As the container gets smaller, the percent available space for atom motion decreases.

  • The observed pressure would be higher than predicted by the Ideal Gas Law due to less volume.

  • The deviation between observed pressure and predicted pressure would increase as the container gets smaller.

  • The deviation from ideal behavior might increase as gas molecules become larger.

  • The data in Model 1 supports the observations and predictions made in previous questions.

Page 5:

  • Model 3 introduces the concept of polarity of gas molecules.

  • H2, CO2, HCI, and NH3 are compared to ideal gas behavior in Model 3.

  • HCI and NH3 are polar molecules, while H2 and CO2 are nonpolar molecules.

  • The volume of gas molecules alone does not fully explain deviations from ideal behavior.

Page 6:

  • Polarity affects the deviation from ideal behavior for a gas

    • In Model 3, polar gases have the opposite relationship between pressure and volume

    • In real gases, molecules have attraction for one another through intermolecular forces

    • Molecules may have a preference for moving towards each other instead of towards the wall of the container

  • Attractions between gas molecules lower the observed pressure compared to that predicted by the Ideal Gas Law

    • Gas molecules tend to be attracted to themselves, causing fewer wall collisions

  • As intermolecular forces between gas molecules become stronger, the deviation between observed pressure and predicted pressure increases

    • Stronger intermolecular forces lead to a greater deviation from ideal gas behavior

  • The effect of intermolecular forces on the pressure of the gas decreases as the volume of the container gets larger

    • As volume increases, the deviation from the Ideal Gas Equation gets smaller

  • Answers to Questions 19-21 are supported by the data in Model 3

    • Polar gases have intermolecular forces, causing lower pressure and greater deviation from ideal gas behavior

Page 7:

  • The graph in Model 1 supports the answer to Question 20

    • As the polarizability of the atom increases, the deviation from the Ideal Gas Law also increases

  • Gases with the smallest deviations from ideal behavior to greatest deviations from ideal behavior:

    • Cl (non-polar), F (non-polar), N (non-polar), O (non-polar)

    • Dispersion forces are the only intermolecular forces present, and more mass leads to greater polarizability

  • The deviation from ideal behavior for a gas increases when more moles of gas are introduced into a more rigid container

    • More moles of gas lead to more intermolecular forces and less available space, increasing the deviation

  • The deviation from ideal behavior for a gas decreases when the gas is at a higher temperature in a rigid container

    • As temperature increases, intermolecular forces decrease, but the effect of volume stays the same, resulting in a decrease in deviation

Page 8:

  • The Van der Waals equation is the Ideal Gas Law equation with correction factors

  • Constants a and b are proportional to the effects of volume and intermolecular forces

  • Constant a adjusts for the reduction of pressure due to attractive forces between gas molecules

  • Constant b adjusts for the reduction of usable volume because gas molecules take up space

  • Carbon dioxide (CO2) has a smaller a constant and a larger b constant compared to ammonia (NH3)

    • Ammonia is more polar than CO2, but less massive and voluminous, resulting in a larger a constant and a smaller b constant

Page 9:

  • Calculation of pressure using the Ideal Gas Law and the Van der Waals equation for a 10.000-L tank of nitrogen with 4.000 moles of gas at 22.00 °C

    • Expected pressure with Ideal Gas Law: 9669 atm

    • Actual pressure with Van der Waals equation: 9.623 atm

  • The anemometer on the tank would need to be precise to the hundredth of an atmosphere to detect a deviation from the pressure calculat