Question

Which physical state is described as having a variable shape and variable volume?

Short answer

Gas has both variable shape and volume.

Step-by-step solution

Identify the States of Matter

There are three primary states of matter: solid, liquid, and gas. Each state has distinct characteristics regarding shape and volume.

Understand the Characteristics of Gases

A gas has neither a definite shape nor a definite volume. Gases take the shape and volume of their container, meaning they are compressible and expandable.

Compare with Other States

A solid has a fixed shape and fixed volume, while a liquid has a variable shape but a fixed volume. Since we are looking for a state with both variable shape and volume, we can eliminate solids and liquids.

Conclusion

From the information provided, a gas is the only state of matter with both a variable shape and volume.

Key concepts

Characteristics of Gases

Gases possess some unique and interesting characteristics that set them apart from solids and liquids. A primary feature is their lack of definite shape and volume. Gases flow freely to fill the entirety of their container, adopting its shape and volume. For instance, when you open a perfume bottle, the scent spreads throughout the room. This happens because gas molecules move rapidly and spread out due to their high kinetic energy.

• Compressibility: Gases can be compressed more than liquids or solids. Applying pressure decreases the space between molecules. That is why we can store large amounts of gases in compressed forms, like helium or oxygen tanks.
• Expandability: Reducing pressure allows gases to expand. This property explains how airbags inflate rapidly during a car accident.
• Diffusion: Gas molecules mix evenly without agitation. Their molecules move at high speeds, leading to rapid distribution and mixing throughout the space available.

Another fascinating feature of gases is their response to changes in temperature and pressure, which is described well by the ideal gas law: \[ PV = nRT \]where \( P \) is pressure, \( V \) is volume, \( n \) is the number of moles, \( R \) is the gas constant, and \( T \) is temperature. This equation gives insights into the behavior of gases in different conditions.

Solid State

The solid state of matter is known for its fixed shape and definite volume. This rigidity comes from the way particles are arranged in a solid. They are closely packed in an orderly fashion, typically in a regular pattern. This results in limited vibration and movement, giving a solid its sturdy form.

• Structure: The particles in solids are tightly bound in a fixed position, often forming geometric patterns that lead to crystalline structures, such as those found in diamonds or table salt.
• Volume Stability: Because of the tightly packed nature of the particles, solids maintain a fixed volume and do not expand like gases do under pressure.
• Low Compressibility: Solids resist compression due to their high-density particle arrangement. Attempting to compress a solid meets with much more resistance compared to gases or liquids.

In addition, solids can be classified into crystalline and amorphous types. Crystalline solids have a well-organized atomic structure, whereas amorphous solids, like glass, lack this specific long-range order.

Liquid State

Liquids have quite a fascinating set of properties that bridge the characteristics between solids and gases. One of their distinctive features is having a definite volume but no fixed shape. They conform to the shape of their container while maintaining a constant volume.

• Fluidity: Molecules in a liquid are less tightly packed than in a solid but more so than in a gas. This allows them to flow and move around each other, which is why liquids can easily pour or spill.
• Surface Tension: Liquids exhibit surface tension, which is the force acting on the surface molecules that causes liquids to minimize surface area. This is why water droplets form beads.
• Viscosity: This refers to the resistance a liquid has to flow. Honey, for example, is more viscous than water because its particles resist movement more.

Liquids respond to changes in temperature by expanding, although not as dramatically as gases. As temperature increases, the kinetic energy of the molecules increases, causing them to move apart and increase in volume.