Final answer:
Gas refers to a substance in the gaseous state at any temperature, while vapor specifically denotes the gaseous state of a substance that is normally a liquid or solid at room temperature, existing as a gas due to heating or decreased pressure, not necessarily at its boiling point.
Step-by-step explanation:
The distinction between gas and vapor can sometimes cause confusion, but it is an important concept in chemistry. A gas is a substance that is naturally in the gaseous state at room temperature, and it will remain a gas under a range of temperatures and pressures.
In contrast, a vapor is the gaseous state of a substance that is a liquid or a solid at room temperature and only exists in the gas phase because it has been temporarily heated or has a pressure reduction, not necessarily at its boiling point.
Therefore, the correct answer to the student's question would be a variant of option a): Gas refers to substances in a gaseous state at any temperature, while vapor specifically denotes a substance in a gaseous state below its boiling temperature.
The term vapor is often used when discussing the process of vaporization (also known as evaporation), which can occur when a liquid's surface molecules absorb energy and transition into the gas phase. This process does not require the liquid to be at its boiling point; it occurs at various temperatures below the boiling point.
When a substance is in a closed container, the vapor can reach an equilibrium pressure known as the vapor pressure. The gas phase is referred to as vapor because it can still condense into a liquid if conditions allow.