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Thermodynamics: Temperature and Phase

Temperature as you know has a direct effect on whether a matter's phase is currently a solid, liquid, or gas. The phase of matter directly relates to the kinetic energy within the molecular bonds and the bond strength. When matter is in a solid phase this means that the molecular bonds between molecules are strong and hold the molecules and atoms closely together. There is however still molecular vibration between the bonds due to kinetic energy. On the other hand when matter is in a liquid phase the molecules and atoms are held together through loose bonds. These bonds are weak enough to cause the fluid molecules to flow over each other when subjected a shear stress of any magnitude. However, when a normal compressible force is applied to the bond the fluid bonds will act as a solid, which is why most fluids are considered incompressible. Finally, gases have enough kinetic energy between molecules and atoms that the molecular bond is not strong enough to hold the atoms together but instead the molecules will bounce around their container randomly. Gases flow like a liquid would flow, but because of their desire to fill their container they are compressible unlike a liquid. Now, all of this relates to temperature because temperature is the measurement of kinetic energy between molecules and can be used to determine when phase changes will occur. The figure below shows the three phases of matter at the molecular level.

phases of matter at the molecular level

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