Question

How does the energy of attraction between particles compare with their energy of motion in a gas and in a solid? As part of your answer, identify two macroscopic properties that differ between a gas and a solid.

Short answer

In a gas, the energy of motion is greater than the energy of attraction, whereas in a solid, the energy of attraction is greater. Gases are less dense and compressible; solids are dense and incompressible.

Step-by-step solution

- Understand Energy of Motion and Energy of Attraction

The energy of motion refers to the kinetic energy possessed by particles due to their movement. The energy of attraction refers to the potential energy due to intermolecular forces that pull particles together.

- Energy of Particles in a Gas

In a gas, particles have high kinetic energy, meaning their energy of motion is significant. The energy of attraction between particles is much weaker compared to their energy of motion due to the larger distances between gas particles.

- Energy of Particles in a Solid

In a solid, particles have low kinetic energy and primarily vibrate in place. The energy of attraction between particles is much stronger in comparison to their energy of motion, keeping the particles in fixed positions.

- Compare Macroscopic Properties

A gas has low density and is compressible, while a solid has high density and is incompressible. These properties arise due to the differences in the energy of motion and energy of attraction among their particles.

Key concepts

Kinetic Energy

Kinetic energy is the energy that particles possess due to their motion. In the context of gases and solids, the kinetic energy of particles varies significantly.

• In gases, particles move quickly and freely, so their kinetic energy is very high. They have enough energy to overcome some of the attractive forces between them.
• In solids, particles are tightly packed and can only vibrate in fixed positions, resulting in much lower kinetic energy. They do not have enough energy to break free from their fixed positions.

Kinetic energy is directly related to temperature. As temperature increases, the kinetic energy of particles also increases since they move faster. This is why heating a solid can turn it into a liquid and then into a gas—because the particles gain enough kinetic energy to move further apart.

Potential Energy

Potential energy in particles is sourced from the intermolecular forces that hold them together. This energy is higher when particles are closer to each other.

• In solids, particles are closely packed, so the potential energy due to intermolecular forces is high. This strong attraction keeps the particles in fixed positions, forming a rigid structure.
• In gases, the particles are much further apart, meaning the potential energy from intermolecular forces is much lower. The weak attraction allows the particles to move freely and independently.

Potential energy affects the state of matter and the phase transitions between solid, liquid, and gas. For instance, when energy is added to a solid, the potential energy decreases as particles gain kinetic energy and start to move apart.

Intermolecular Forces

Intermolecular forces are the forces of attraction or repulsion between neighboring particles (atoms, molecules, or ions). These forces are crucial in determining the states of matter and their properties.

• In solids, intermolecular forces are strong. These forces keep the particles in close contact, hence the solid's fixed shape and high density. For example, ionic bonds in salts have strong electrostatic attractions that hold the ions in a rigid lattice.
• In gases, intermolecular forces are weak. This weak attraction does not hold the particles close together, allowing them to move freely. As a result, gases can expand to fill any container and have low density.

The strength of these forces depends on the type of particles and the distance between them. For instance, Van der Waals forces, dipole-dipole interactions, and hydrogen bonds are some types of intermolecular forces influencing the behavior of different substances.

Macroscopic Properties

Macroscopic properties are the observable characteristics of a material as a whole, which arise from the behavior of particles at the microscopic level. These properties help us differentiate between solids, liquids, and gases.

• In gases, two notable macroscopic properties are low density and high compressibility. The significant kinetic energy and weak intermolecular forces allow gas particles to spread far apart, making gases less dense and easy to compress.
• In solids, the two key macroscopic properties are high density and incompressibility. Strong intermolecular forces keep particles in close proximity and fixed positions, resulting in a dense and rigid structure that cannot be easily compressed.

Understanding these properties is essential for predicting the behavior of materials under different conditions. For example, the knowledge that gases are compressible leads to their use in pneumatic systems, whereas the rigidity of solids makes them suitable for construction and manufacturing.