Question

Is the density of a gaseous substance larger or smaller than the density of a liquid or a solid at the same temperature? Why?

Short answer

The density of a gaseous substance is smaller than that of a liquid or solid at the same temperature. This is because the particles in the gaseous state are farther apart due to their higher kinetic energy, which causes them to move more rapidly and spread out, occupying more space than particles in the solid or liquid states.

Step-by-step solution

States of Matter and Density

Densities of substances can vary depending on the state of matter they are in: solid, liquid, or gas. In general, solids have the highest density, followed by liquids, with gases having the lowest density. The main factor influencing the density of a substance in different states is the spacing between the particles (atoms, molecules, or ions) making up the substance.

Particle Spacing

In general, particles in solids are very close together and have a regular arrangement. In liquids, particles are also close together but have a less regular arrangement, allowing them to flow and take the shape of their container. In gases, particles are much farther apart compared to solids and liquids and move randomly, occupying all available space. At the same temperature, the particles of a gaseous substance have more kinetic energy compared to particles in solid or liquid states, causing them to move away from each other.

Density Comparison

Now that we know the differences in particle spacing for solids, liquids, and gases, we can determine which substance has a larger or smaller density at the same temperature. Since particles in a gaseous substance are more spread out and occupy more space compared to particles in a solid or liquid state, a gaseous substance will have a smaller density compared to a liquid or solid at the same temperature.

Explanation

The density of a gaseous substance is smaller than that of a liquid or solid at the same temperature because the particles in the gaseous state are farther apart, providing more space between them. This increased spacing is due to the higher kinetic energy of the particles in the gaseous state, as they move more rapidly and spread out to occupy the available space.

Key concepts

States of Matter

Matter exists in three primary states: solid, liquid, and gas. These states are defined by the arrangement and movement of their particles. In solids, particles are tightly packed together in a fixed structure, which gives solids their definite shape and volume. Liquids have particles that are still close, but they can flow past one another, which allows liquids to take the shape of their container while maintaining a constant volume. Gases, unlike solids and liquids, have particles that are spaced far apart. This causes gases to expand and fill the whole volume of their container.

• Solid: Fixed shape, fixed volume, particles closely packed.
• Liquid: Takes shape of container, fixed volume, particles less tightly packed.
• Gas: Takes shape and volume of container, particles very far apart.

These differences in particle arrangement and movement explain why the density of solids, liquids, and gases varies significantly.

Kinetic Energy

Kinetic energy refers to the energy that particles possess due to their motion. This energy significantly impacts how particles behave in different states of matter. In solids, kinetic energy is relatively low. Particles vibrate but largely retain their fixed positions. In liquids, particles have more kinetic energy, which allows them to move around and slide past each other, causing the liquid to flow. Gases exhibit the highest kinetic energy among the three states. Here, particles move rapidly in all directions, resulting in much greater distances between them.

This increase in kinetic energy from solid to liquid to gas accounts for the changes in particle behavior and spacing:

• Solid: Low kinetic energy, restricted to vibrations.
• Liquid: Moderate kinetic energy, allows flowing motion.
• Gas: High kinetic energy, free movement in all directions.

Understanding kinetic energy is crucial to comprehending why gases, with their higher energy, tend to have lower densities than liquids or solids.

Particle Spacing

Particle spacing is the distance between individual particles in a substance. This spacing plays a key role in determining the density of a substance. In solids, particles are packed closely in a defined pattern, with very little space between them, which contributes to the higher density. Liquids have particles that are close together but not in a fixed pattern, allowing for some movement and more space compared to solids, resulting in moderate density. For gases, particles are widely spaced with no fixed arrangement, leading to much lower density.

The large particle spacing in gases means more space between individual particles, which reduces the overall density of the substance. This is contrasted with the compressed and structured arrangement in solids and the intermediate spacing in liquids:

• Solid: Closely-packed, fixed arrangement.
• Liquid: Close but fluid, less structured.
• Gas: Widely spaced, no fixed pattern.

This understanding clarifies why gaseous substances have notably lower densities compared to their liquid and solid counterparts.