key term - Van der Waals equation

Definition

The van der Waals equation is a mathematical model that describes the behavior of real gases by accounting for the finite size of molecules and intermolecular forces. It modifies the Ideal Gas Law to better predict gas behavior under high pressure and low temperature conditions.

5 Must Know Facts For Your Next Test

1. The van der Waals equation is given by: $\left( P + \frac{a}{V_m^2} \right) (V_m - b) = RT$, where $P$ is pressure, $V_m$ is molar volume, $T$ is temperature, $R$ is the gas constant, and $a$ and $b$ are empirical constants specific to each gas.
2. The term $\frac{a}{V_m^2}$ accounts for intermolecular attractions which reduce pressure.
3. The term $b$ corrects for the finite volume occupied by gas molecules.
4. As temperature increases or at low pressures, real gases behave more like ideal gases, making the adjustments in the van der Waals equation less significant.
5. Values of $a$ and $b$ can be experimentally determined and differ from one gas to another.

Review Questions

Related terms

Ideal Gas Law:

A relation between pressure ($P$), volume ($V$), amount of substance ($n$), and temperature ($T$) given by: $PV = nRT$. This law assumes no intermolecular forces and negligible molecular volume.

Boyle's Law:

A gas law stating that the pressure of a given mass of gas is inversely proportional to its volume at constant temperature.

Intermolecular Forces:

Forces of attraction or repulsion between neighboring particles (atoms, molecules, or ions). These include Van der Waals forces, dipole-dipole interactions, and hydrogen bonding.