Science, Tech, Math › Science Critical Point Definition What Is the Critical Point in Chemistry? Share Flipboard Email Print This is a phase diagram, which includes the critical point and triple point. Booyabazooka, Wikipedia Commons Science Chemistry Chemical Laws Basics Molecules Periodic Table Projects & Experiments Scientific Method Biochemistry Physical Chemistry Medical Chemistry Chemistry In Everyday Life Famous Chemists Activities for Kids Abbreviations & Acronyms Biology Physics Geology Astronomy Weather & Climate By Anne Marie Helmenstine, Ph.D. Chemistry Expert Ph.D., Biomedical Sciences, University of Tennessee at Knoxville B.A., Physics and Mathematics, Hastings College Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels. our editorial process Facebook Facebook Twitter Twitter Anne Marie Helmenstine, Ph.D. Updated March 10, 2018 Critical Point Definition In a phase diagram, The critical point or critical state is the point at which two phases of a substance initially become indistinguishable from one another. The critical point is the end point of a phase equilibrium curve, defined by a critical pressure Tp and critical temperature Pc. At this point, there is no phase boundary. Also Known As: critical state Critical Point Examples The liquid-vapor critical point is the most common example, which is at the end point of the pressure-vapor temperature curve distinguishing a substance's liquid and vapor. The meniscus between steam and water vanishes at temperatures above 374°C and pressures above 217.6 atm, forming what is known as a supercritical fluid. There is also a liquid-liquid critical point in mixtures, which occurs at the critical solution temperature.