Question

1. the state of a substance can change when the substance is heated or cooled. so what does it mean to say that a certain substance is a solid, liquid, or gas?

Explanation:

To determine what it means for a substance to be a solid, liquid, or gas, we analyze the molecular arrangement and properties:

• Solid: Molecules are closely packed in a fixed, ordered structure. This gives solids a definite shape and volume, with strong intermolecular forces holding the molecules in place. For example, a diamond has a rigid, crystalline structure.
• Liquid: Molecules are close together but can move past one another. Liquids have a definite volume but take the shape of their container, as the intermolecular forces are weaker than in solids but stronger than in gases. Water is a common liquid where molecules can flow.
• Gas: Molecules are far apart and move freely and rapidly. Gases have neither a definite shape nor volume, filling the entire space of their container. The intermolecular forces are very weak. Air (a mixture of gases) expands to fill any container.

These states are defined by the arrangement, movement, and forces between the molecules of the substance, which are influenced by temperature and pressure (related to heating/cooling as mentioned in the question).

Answer:

• Solid: Molecules are closely packed in a fixed, ordered structure, giving a definite shape and volume.
• Liquid: Molecules are close but move past each other, having a definite volume but taking the container’s shape.
• Gas: Molecules are far apart, move freely, and have neither definite shape nor volume.

(These definitions relate to molecular arrangement, movement, and intermolecular forces, influenced by heating/cooling.)