Which equation accounts for molecular size and intermolecular forces when modeling gases?

Which equation accounts for molecular size and intermolecular forces when modeling gases?

• A. Ideal gas law
• B. van der Waals equation
• C. Boyle's law
• D. Charles' law

Answer: (B)

Real gas behavior requires corrections to the ideal gas law to reflect molecular size and intermolecular forces. The van der Waals equation adds two correction terms: a for the attractive forces between molecules and b for the finite volume occupied by the molecules themselves. In molar form, (P + a/V_m^2)(V_m - b) = RT, where V_m is the molar volume. The a term lowers the pressure to account for intermolecular attractions, while the b term reduces the effective volume to account for the space that molecules themselves occupy. At low pressures and high temperatures, these corrections become negligible, and the equation reduces to the ideal gas law, P V = RT, highlighting why the van der Waals form is used when size and interactions matter. The other laws—Boyle's and Charles'—describe relationships for ideal gases under specific conditions and do not incorporate molecular size or intermolecular forces.

Real gas behavior requires corrections to the ideal gas law to reflect molecular size and intermolecular forces. The van der Waals equation adds two correction terms: a for the attractive forces between molecules and b for the finite volume occupied by the molecules themselves. In molar form, (P + a/V_m^2)(V_m - b) = RT, where V_m is the molar volume. The a term lowers the pressure to account for intermolecular attractions, while the b term reduces the effective volume to account for the space that molecules themselves occupy. At low pressures and high temperatures, these corrections become negligible, and the equation reduces to the ideal gas law, P V = RT, highlighting why the van der Waals form is used when size and interactions matter. The other laws—Boyle's and Charles'—describe relationships for ideal gases under specific conditions and do not incorporate molecular size or intermolecular forces.