Deviation from Ideal Gas Law - AP Chemistry

1. Identify a gas that behaves nearly ideally under ordinary conditions.

   Helium. Small, light atoms with weak intermolecular forces.

2. Find the pressure correction in Van der Waals equation for $1 \text{mol}$ of gas.

   $\frac{a}{V^2}$. For 1 mole, $n = 1$, so the correction becomes $\frac{a}{V^2}$.

3. What is the Van der Waals equation?

   $(P + \frac{an^2}{V^2})(V - nb) = nRT$. Modified ideal gas law accounting for real gas behavior.

4. What does a high value of 'a' indicate in Van der Waals equation?

   Strong intermolecular forces. Large 'a' means strong attractive forces between molecules.

5. Provide the value of the universal gas constant 'R'.

   $R = 0.0821 \frac{L \times atm}{mol \times K}$. The standard value used in gas law calculations.

6. How does Van der Waals equation modify the Ideal Gas Law?

   Corrects for volume and pressure deviations. Adds corrections for molecular size and intermolecular forces.

7. State the definition of an ideal gas.

   An ideal gas perfectly follows the Ideal Gas Law. A theoretical gas that obeys all gas law assumptions perfectly.

8. What is the primary cause of deviation at low temperatures?

   Increased intermolecular attractions. Lower temperatures enhance attractive forces between gas molecules.

9. Name another condition for deviation from ideal behavior.

   Low temperature. Reduces kinetic energy, allowing intermolecular forces to dominate.

10. What is the Ideal Gas Law equation?

    $PV = nRT$. The fundamental relationship between pressure, volume, moles, and temperature.

11. What is the primary focus of the Van der Waals equation?

    Correcting Ideal Gas Law for real gases. Modifies ideal gas law to account for real gas behavior.

12. What is the significance of 'R' in the Ideal Gas Law?

    'R' is the universal gas constant. A proportionality constant linking pressure, volume, moles, and temperature.

13. Calculate pressure deviation using $P = 4 \text{atm}$, $a = 0.8$, $V = 20 \text{L}$.

    $\text{Deviation} = \frac{0.8}{20^2}$. Pressure correction term: $\frac{a}{V^2}$ for 1 mole of gas.

14. What does 'a' in Van der Waals equation account for?

    Intermolecular attraction forces. Parameter representing strength of intermolecular attractive forces.

15. Identify another assumption of the Ideal Gas Law.

    Gas particles exert no intermolecular forces. Assumes no attractive or repulsive forces between particles.

16. What is the effect of molecular size on gas deviation?

    Larger size increases deviation. Larger molecules occupy more space, increasing deviation from ideality.

17. Identify a situation where Ideal Gas Law fails.

    At very high pressures. Extreme pressure makes particle volume and forces significant.

18. What is the effect of intermolecular forces on gas pressure?

    Decreases observed pressure. Attractive forces reduce pressure exerted on container walls.

19. What does the term $nb$ in Van der Waals equation represent?

    Volume occupied by gas particles. Total volume excluded due to finite molecular size.

20. What is the main limitation of the Ideal Gas Law?

    Assumes no volume and no interactions between particles. Ignores real effects: molecular size and intermolecular forces.

21. Name a condition under which real gases deviate from ideal behavior.

    High pressure. Forces particles closer, making volume and intermolecular forces significant.

22. Calculate $n$ if $P = 3 \text{atm}$, $V = 10 \text{L}$, $T = 400 \text{K}$, $R = 0.0821$.

    $n = \frac{PV}{RT} = 0.914 \text{mol}$. Using $n = \frac{PV}{RT}$ with given values yields 0.914 mol.

23. What effect does increasing pressure have on gas behavior?

    Gases deviate more from ideal behavior. Higher pressure compresses gas, making particle volume more significant.

24. Calculate corrected pressure using $P = 3 \text{atm}$, $a = 0.5$, $V = 10 \text{L}$.

    $P' = 3 + \frac{0.5}{10^2} = 3.005 \text{atm}$. Adding pressure correction: $P + \frac{an^2}{V^2}$ for $n=1$.

25. What correction does $b$ account for in the Van der Waals equation?

    Volume of gas particles. The finite size of gas molecules reduces available volume.

26. Calculate $T$ if $P = 2 \text{atm}$, $V = 5 \text{L}$, $n = 1 \text{mol}$, $R = 0.0821$.

    $T = \frac{PV}{nR} = 121.95 \text{K}$. Rearranging ideal gas law: $T = \frac{PV}{nR}$ gives 121.95 K.

27. Identify the correction factor for intermolecular forces in Van der Waals.

    $\frac{an^2}{V^2}$. Accounts for attractive forces reducing observed pressure.

28. Calculate $P$ if $V = 10 \text{L}$, $n = 1 \text{mol}$, $T = 300 \text{K}$, $R = 0.0821$.

    $P = \frac{nRT}{V} = 2.463 \text{atm}$. Using $P = \frac{nRT}{V}$ with given values yields 2.463 atm.

29. Which gas law relates pressure and volume at constant temperature?

    Boyle's Law. States that $PV$ is constant at fixed temperature.

30. What happens to $PV/nRT$ for an ideal gas?

    Equals 1. Compressibility factor equals 1 for perfect ideal behavior.

31. Name one assumption of the Ideal Gas Law.

    Gas particles have no volume. Assumes particles are point masses with negligible size.

32. What modification do real gases have compared to ideal gases?

    Non-zero volume and intermolecular forces. Real gases have finite size and experience intermolecular attractions.

33. Which real gas behavior is corrected by the term $(P + \frac{an^2}{V^2})$?

    Pressure correction for intermolecular forces. Accounts for reduced pressure due to intermolecular attractions.

34. Identify the term for the effective volume in Van der Waals equation.

    $V - nb$. Available volume after subtracting space occupied by gas particles.

35. What effect does increasing pressure have on gas behavior?

    Gases deviate more from ideal behavior. Higher pressure compresses gas, making particle volume more significant.

36. What happens to gas particles at low temperatures?

    Intermolecular forces become significant. Reduced kinetic energy allows attractive forces to affect behavior.

37. Which gas law relates volume and temperature at constant pressure?

    Charles's Law. States that $V/T$ is constant at fixed pressure.

38. State the critical temperature's influence on gas behavior.

    Above it, gases behave more ideally. Higher temperatures overcome intermolecular forces, approaching ideal behavior.

39. Calculate volume if $P = 1 \text{atm}$, $n = 1 \text{mol}$, $T = 273 \text{K}$, $R = 0.0821$.

    $V = \frac{nRT}{P} = 22.414 \text{L}$. Standard molar volume calculation at STP conditions.

40. What causes real gases to deviate from ideal behavior at high pressures?

    Finite volume of gas particles. Molecular volume becomes significant fraction of container volume.

Study these flashcards