The van der Waals equation modifies the ideal gas law to account for

Answer: Real gas attractions (a) and finite molecular volume (b) (P + an²/V²)(V − nb) = nRT. Reduces to PV = nRT when a, b → 0.

The dip below the ideal line at moderate pressure is best explained by:

Answer: Attractive intermolecular forces dominating At moderate P, attractive IMFs reduce effective pressure, lowering Z = PV/nRT below 1. At very high P, particle volume dominates and Z exceeds 1.

Real gases deviate most from ideal behavior at

Answer: Low temperature, high pressure (when IMFs and molecular volumes become significant) Low T → IMFs cause attractions; high P → molecule volume is no longer negligible relative to container.

AP Chemistry · Topic 3.6

Deviations from Ideal Gas Behavior Practice

Part of Properties of Substances and Mixtures.(SAP-7.D)

Practice questions

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Sample questions

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Sample 1difficulty 3/5
$The van der Waals equation modifies the ideal gas law to account for$
- A
  $Real gas attractions (a) and finite molecular volume (b)$
  check_circle
- B
  $Photon emission$
- C
  $Quantum effects$
- D
  $Heat transfer$
Why
$(P + an²/V²)(V - nb) = nRT. Reduces to PV = nRT when a, b \to 0.$
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Sample 2difficulty 3/5
$Compressibility factor Z = PV/nRT is plotted against pressure for a real gas.$
$The dip below the ideal line at moderate pressure is best explained by:$
- A
  $Elastic collisions only$
- B
  $Attractive intermolecular forces dominating$
  check_circle
- C
  $High temperature$
- D
  $Negligible particle volume$
Why
$At moderate P, attractive IMFs reduce effective pressure, lowering Z = PV/nRT below 1. At very high P, particle volume dominates and Z exceeds 1.$
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Sample 3difficulty 3/5
$Real gases deviate most from ideal behavior at$
- A
  $High temperature, low pressure$
- B
  $Standard conditions$
- C
  $Vacuum$
- D
  $Low temperature, high pressure (when IMFs and molecular volumes become significant)$
  check_circle
Why
$Low T \to IMFs cause attractions; high P \to molecule volume is no longer negligible relative to container.$
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Sample 4difficulty 4/5
$Real gases deviate MOST from ideal-gas behavior at$
- A
  $Low temperature, high pressure (intermolecular forces and finite volume matter)$
  check_circle
- B
  $Any conditions equally$
- C
  $High temperature, low pressure$
- D
  $Standard conditions$
Why
$At low T molecules move slowly (IMF matters); at high P molecules are crowded (finite volume matters).$
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Sample 5difficulty 4/5
$Real gases deviate most from ideal-gas behavior at$
- A
  $Low pressure and high temperature$
- B
  $STP exactly$
- C
  $High pressure and low temperature$
  check_circle
- D
  $Conditions where Kelvin equals 1$
Why
$Ideal gas assumes negligible volume + no intermolecular forces. High P (compression) + low T (slow molecules) make finite molecular volume and attractions matter — biggest deviations.$
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