Final answer:
Exceeding the critical point of a substance results in the formation of a supercritical fluid, where the liquid and gas phases are indistinguishable. At temperatures higher than the critical temperature, no amount of pressure can liquefy a gas.
Step-by-step explanation:
When pressure and temperature exceed the critical point of a substance, the distinction between the liquid and gas phases disappears, and a new phase called a supercritical fluid is formed. At temperatures above the critical temperature (Tc), a gas cannot be liquefied, no matter how much pressure is applied, because the kinetic energy of the molecules is too high for the intermolecular forces to bring them into a liquid state. The physical properties of a supercritical fluid are intermediate between those of a gas and a liquid. This unique state of matter allows the supercritical fluid to flow through solids like a gas and dissolve materials like a liquid.
For water, for example, the critical temperature is 373.99°C, and the critical pressure is 217.75 atm. Beyond these critical points, water becomes a supercritical fluid, unable to exhibit distinct liquid or vapor phases, regardless of the pressure applied. Substances with strong intermolecular forces have higher critical temperatures, whereas those with weaker intermolecular forces exhibit lower critical temperatures and thus, lower critical points.