What is meant by the term "change of state"?

• A. A change in the pressure of a gas
• B. A change from one phase to another: solid, liquid, or gas
• C. A change in temperature without a phase change
• D. A change in chemical composition of a substance

Answer: (B)

The term "change of state" refers specifically to the transition of a substance from one phase to another, which can be solid, liquid, or gas. This process involves the rearrangement of molecules and the energy changes associated with these transformations. For example, when ice (solid) melts into water (liquid), or when water boils into steam (gas), these are both examples of changes of state.

Understanding this concept is fundamental in various fields, particularly in thermodynamics, where the behavior of substances under different temperatures and pressures is crucial. The other choices provide different types of changes but do not accurately define change of state. Changes in pressure or temperature can affect states but do not, in themselves, define a phase transition. Similarly, a change in chemical composition involves alterations at the molecular level rather than a shift between solid, liquid, or gas phases.