The three fundamental phases of matter are solid, liquid and gas. A phase change occurs when a substance transitions from one phase to another. In everyday life, phase changes -- such as liquid water boiling into steam -- are caused by increasing or decreasing temperature, but pressure is equally capable of inducing a phase change. The combined effects of temperature and pressure lead to a condition in which the three phases of matter can coexist.
One Substance, Three Phases
A phase diagram is a valuable tool for analyzing the influence of temperature and pressure on phase changes. With pressure on the vertical axis and temperature on the horizontal axis, a phase diagram uses curved lines to depict the temperature and pressure conditions that result in phase changes. A phase diagram has three lines that depict the temperature-pressure combinations resulting in a transition from solid to liquid, liquid to gas, and solid to gas. The point at which these three lines intersect is called the triple point -- at this exact combination of temperature and pressure, a substance can assume any of the three phases. The triple point for water is a temperature of 0.01 degrees Celsius (32.018 degrees Fahrenheit) and a pressure of 611.7 Pascals (.006 atmospheres). With this combination of temperature and pressure, water can exist as liquid water, ice or steam.
About the Author
Joseph West has been writing about engineering, agriculture and religion since 2006. He is actively involved in the science and practice of sustainable agriculture and now writes primarily on these topics. He completed his copy-editing certificate in 2009 and holds a Bachelor of Science degree from the University of California-San Diego.