Question

If the assumption that there is no force of attraction between the molecules of a gas is correct, what will be the consequences? (a) All gases will be ideal gases. (b) The gases will never liquefy when cooled and compressed. (c) Gases will have definite volume. (d) Gases will occupy a definite space.

Short answer

If there is no force of attraction between the molecules of a gas, all gases will behave as ideal gases (a), and they will not liquefy when cooled and compressed (b). Gases will not have a definite volume (c) nor will they occupy a definite space (d), but will expand to fill their container.

Step-by-step solution

Understanding the Kinetic Molecular Theory

This step is to understand the basic tenets of the Kinetic Molecular Theory (KMT), which describes the behavior of ideal gases. According to KMT, particles of an ideal gas move in constant, random motion and do not exert forces of attraction or repulsion on one another except during collisions, where they exert a perfectly elastic collision, meaning no energy is lost. If there is no force of attraction between the gas molecules, this aligns with one of the assumptions made in the theory about ideal gases.

Implications of No Attraction Force for Gases

Analyze the implications of having no force of attraction between the molecules of a gas. The absence of intermolecular forces amongst gas molecules would mean that the molecules are independent of each other, which is a characteristic of ideal gases. Consequently, all gases would behave as ideal gases because they would not deviate from ideal gas behavior by condensing to a liquid or exhibiting non-ideal pressure-volume-temperature relationships.

Consequences on Gas Liquefaction

If there is no force of attraction between gas molecules, the gases would not condense into a liquid form when cooled or compressed. This is because liquefaction occurs when the molecules are close enough that their intermolecular forces hold them together in a liquid state. In the absence of these forces, even under conditions of low temperature or high pressure, the gases would remain in the gaseous state.

Gas Volume and Space Occupation

Having no force of attraction between gas molecules would mean that the molecules are free to move and expand to fill any container fully. Therefore, gases will not have a definite volume nor occupy a definite space because they will always expand to fill the entirety of their container. The volume and shape of a gas are, therefore, not fixed but are shaped by its container.

Key concepts

Kinetic Molecular Theory

The Kinetic Molecular Theory (KMT) offers a fundamental explanation of gas behavior based on the motion of particles. It assumes that gas molecules are small and constantly moving in random directions with various speeds. These molecules are in constant motion and collisions between them are perfectly elastic—no energy is lost in the process. The KMT also posits that the average kinetic energy of the gas molecules is directly proportional to the temperature of the gas.

Under this theory, because the particles are so far apart relative to their size, the theory suggests negligible intermolecular forces, aligning perfectly with the proposition that there are no forces of attraction between the molecules. This is a cornerstone for understanding why, under KMT, gases don't condense into liquids under normal circumstances—they simply don't attract each other enough to do so.

Intermolecular Forces

Intermolecular forces are the forces of attraction and repulsion between interacting particles (atoms, molecules, or ions). They are responsible for the behavior of substances in different states of matter. These forces can be van der Waals forces, such as dispersion (or London dispersion), dipole-dipole, and hydrogen bonds. In gases, these forces are generally weak because the particles are far apart.

Understanding these forces helps explain why real gases can deviate from ideal behavior. When gas particles are compressed or cooled, they come closer together, and the intermolecular forces become significant, often leading to liquefaction as the particles will attract each other enough to stick together. However, if it's assumed that these forces are non-existent, like in an ideal gas scenario, gases wouldn't liquefy regardless of the pressure or temperature changes.

Gas Liquefaction

Gas liquefaction refers to the process of turning a gas into a liquid. For this to happen, the gas must be cooled and/or pressurized so that the molecules are close enough for their intermolecular forces to be effective. During liquefaction, the kinetic energy of the molecules decreases, and their velocity reduces to the extent that the attractive forces exceed the energy causing them to repel each other.

If gas molecules had no force of attraction, no amount of cooling or compression would lead to liquefaction since the basic requirement for the process—the intermolecular forces—is absent. This concept is fundamental when considering the physical properties of gases and the conditions required to change them into liquids or solids.

Properties of Gases

Gases have distinct properties that differentiate them from liquids and solids. They have neither a fixed shape nor a fixed volume. Instead, they tend to expand and completely fill any container they are in, taking the shape of that container. The molecules are spaced far apart and are in constant, rapid motion. This behavior is a direct result of the weak intermolecular forces present in the gas phase and is described by the gas laws—such as Boyle's, Charles's, and Avogadro's laws.

When considering ideal gases, these properties are observed under the assumption that the molecules do not interact with one another aside from elastic collisions. Thus, ideal gases can be compressed much more than liquids or solids, and they expand when the temperature increases due to their molecular freedom, a hallmark of their behavior that is integral to understanding gas laws and the kinetic molecular theory.