Question

Does the effect of intermolecular attraction on the properties of a gas become more significant or less significant if (a) the gas is compressed to a smaller volume at constant temperature; (b) the temperature of the gas is increased at constant volume?

Short answer

In summary, the effect of intermolecular attraction on the properties of a gas becomes more significant when the gas is compressed to a smaller volume at constant temperature, due to the particles being closer together. However, in the case of increasing temperature at constant volume, the effect of intermolecular attraction becomes less significant, as the energetic collisions between particles cause more distance between them, making the gas resemble an ideal gas.

Step-by-step solution

Understanding intermolecular forces

Intermolecular forces are the forces that exist between molecules. These forces can affect the properties of a substance, including its phase, solubility, and boiling and melting points. In gases, the intermolecular forces are typically weak compared to solids and liquids, because gas particles are farther apart from one another. However, when the conditions change, these forces can become more significant.

Scenario (a): Compressing the gas at constant temperature

When a gas is compressed to a smaller volume at constant temperature, the particles are forced into a smaller space and become closer together. This results in an increase in the frequency and strength of intermolecular collisions/interactions. Consequently, the effect of intermolecular attraction becomes more significant as gas is compressed. The gas particles are now close enough to feel each other's presence, and their motion may be influenced by the attractive forces between them. This will lead to deviation from the ideal behavior (predicted by the Ideal Gas Law) and the gas will exhibit more "real" behavior.

Scenario (b): Increasing temperature at constant volume

In the case where temperature is increased while keeping the volume constant, the average kinetic energy of the gas particles also increases (since temperature is proportional to the average kinetic energy). This means the particles are moving faster and the collisions between them become more energetic. Since the intensity of intermolecular forces depends on the distance between particles (it decreases with the increase in distance), the increase in the temperature causes a decrease in the intermolecular force due to the higher energy of the particles, which leads to more distance between them. As a result, the effect of intermolecular attraction becomes less significant when the temperature of the gas is increased at a constant volume. The gas will act more like an ideal gas and less like a "real" gas.