What property do pure substances exhibit when melted or boiled?

Pure substances have distinct melting and boiling points, which are characteristics that set them apart from mixtures. When a pure substance is heated, it will transition from solid to liquid at its melting point, and from liquid to gas at its boiling point. These phase changes occur at specific temperatures that are unique to each pure substance, providing a reliable means of identifying and characterizing them.

For example, pure water consistently boils at 100 degrees Celsius at standard atmospheric pressure and melts at 0 degrees Celsius. This specificity is crucial in scientific contexts, as it allows for the precise control and prediction of states of matter during experiments and industrial processes.

In contrast, mixtures do not have a sharp melting or boiling point; rather, they have a range of temperatures over which they may change states. This variability arises because mixtures consist of multiple components that can each have different characteristics influencing their overall behavior when heat is applied. Thus, the ability of pure substances to melt and boil at specific temperatures is a defining characteristic that is essential to both practical applications and theoretical understanding in the study of materials.