Question

What is the relationship between thermal energy and intermolecular interaction energy of a substance in three states in terms of \(X\) and \(Y ?\) Gas \(\longrightarrow\) Liquid \(\longrightarrow\) Solid (a) \(X\)-Thermal energy, \(Y\)-Intermolecular interactions (b) \(X\)-Thermal energy, \(Y\)-Thermal energy (c) \(X\)-Intermolecular interactions, \(Y\)-Thermal energy (d) \(X\)-Intermolecular interactions, \(Y\)-Intermolecular interactions

Short answer

(a) X-Thermal energy decreases, Y-Intermolecular interactions increase, as we go from Gas to Liquid to Solid.

Step-by-step solution

Understanding the Problem

The problem requires understanding the relationship between thermal energy and intermolecular interaction energy as a substance changes state from gas to liquid to solid. The options given suggest different relationships between thermal energy (X) and intermolecular interactions (Y).

Analyzing State Transition from Gas to Liquid to Solid

In the transition from gas to liquid to solid, the thermal energy of the substance decreases, which is observed through a lowering of the substance's temperature upon cooling. Concurrently, the strength of intermolecular interactions increases, as molecules come closer together and bond more tightly from gas to liquid to solid phase.

Interpreting the Relationship between Thermal Energy and Intermolecular Interactions

These changes indicate that as thermal energy (X) decreases, intermolecular interaction energy (Y) increases. This is because the decrease in thermal energy reduces the kinetic energy of the particles, allowing the intermolecular forces to bring them closer together, thus increasing the intermolecular interactions.

Identifying the Correct Option

Since thermal energy corresponds to the motion and kinetic energy of the particles, and intermolecular interactions refer to the forces between the particles, the correct relationship between the two is that as one (X) decreases, the other (Y) increases. Hence, the correct option should reflect X as thermal energy and Y as intermolecular interaction energy.

Key concepts

Thermal Energy

In the context of matter and its states, thermal energy refers to the amount of kinetic energy possessed by the particles in a substance. The particles in matter—whether they be atoms or molecules—are always in motion, vibrating or moving about freely, depending on the state of matter. In a solid, particles are closely packed and vibrate in place while in liquids, they move more freely around each other. In gases, particles move about most freely as they have the highest amount of thermal energy.

As we adjust the temperature, we essentially add or remove thermal energy from the system. Heating a substance increases its thermal energy, causing the particles to move more vigorously. Conversely, cooling a substance decreases its thermal energy, which diminishes the movement of the particles. This adjustment in thermal energy can lead to a state transition as the kinetic energy of the particles increases or decreases enough to change the structure of the matter.

Intermolecular Interactions

Intermolecular interactions are the forces that act between particles within a substance, such as atoms or molecules. These forces vary in strength and type and are crucial in determining the physical properties of a state of matter. In a solid, these interactions are strongest, binding the particles tightly in a fixed arrangement. As we transition to a liquid, these forces are weakened; particles are still attracted to each other, but with more freedom to move around. In gases, intermolecular interactions are minimal, allowing particles to roam independently.

Introducing or reducing thermal energy can disrupt or enhance these intermolecular interactions. When a substance heats up and gains thermal energy, the increased motion of particles can overcome the intermolecular forces, potentially causing a phase change. On the flip side, cooling a substance can enhance these interactions as particles lose energy and move less, leading them to come closer together.

State Transition

A state transition, or phase transition, happens when a substance changes from one state of matter to another, such as from a gas to a liquid or from a liquid to a solid. This transformation corresponds to changes in both thermal energy and intermolecular interactions. Upon cooling, a gas may condense to form a liquid as thermal energy decreases and intermolecular attractions become stronger, drawing particles closer together. Similarly, a liquid might freeze into a solid when further cooled, as the motion of its particles decreases sufficiently for fixed bonds to form.

To understand the process of state transition, it's essential to consider both the kinetic interactions of particles and the strength of the bonds between them. This dual perspective helps explain the myriad of properties we observe in materials as they move between different states.

Phase Change

A phase change is the physical process of transition between different states of matter. Examples of phase changes include melting (solid to liquid), freezing (liquid to solid), vaporization (liquid to gas), condensation (gas to liquid), and sublimation (solid to gas). These changes are not random but are dictated by variations in thermal energy and intermolecular interactions within a substance.

When we examine phase changes closely, we see that they usually involve the absorption or release of energy, known as latent heat. For instance, the melting of ice requires the absorption of energy to break the intermolecular bonds holding the water molecules in a solid structure. In contrast, the freezing of water releases energy as water molecules form a solid, and their movement becomes highly restricted. These processes are fundamental examples of how thermal energy and intermolecular forces are intertwined in the behavior of matter.