Final answer:
A phase diagram is a chart that indicates the physical states of a substance at different temperatures and pressures, highlighting the triple point and critical point where phases coexist in equilibrium or change states.
Step-by-step explanation:
A phase diagram is a graphical representation that shows the conditions of temperature and pressure under which a substance exists in different states or phases (solid, liquid, and gas) in a closed system. The diagram includes lines that indicate the conditions where two phases coexist in equilibrium. Key points on this diagram are the triple point, where all three phases (solid, liquid, and gas) coexist in equilibrium, and the critical point, beyond which the distinction between gas and liquid phases ceases to exist and a supercritical fluid is formed. There are four distinct regions in a phase diagram representing the solid, liquid, gas, and supercritical fluid phases.
In a one-component phase diagram, we examine the relationship among the solid, liquid, and gas states of a single substance as a function of temperature and pressure. The phase diagram provides a comprehensive overview of how a substance's physical state can change due to variations in temperature and pressure. By studying a phase diagram, one can predict the phase transitions that a substance may undergo under different conditions.