This video clip explores the process of evaporation and also the meaning of temperature. It deserve to be used as a supplement to one investigation, or may stand ~ above its very own to introduce a lesson or prolong student learning.

You are watching: The average kinetic energy of particles in a substance


Ah, the humble thermometer. Even if it is we want to know if our vacation turkey is cook or if we need concrete proof the we’re as well sick to attend school, a thermometer is the precise scientific tool we need. Yet what, exactly, go a thermometer measure? In various other words, what is temperature, really?


Whether the solid, liquid, or gas, all matter is comprised of atoms and also molecules. These particles space constantly in motion. They collide with each other and also with the walls of anything castle are consisted of in. Us quantify the activities of the particles by their kinetic energies.

In chemistry, we specify the temperature the a substance together the typical kinetic power of every the atoms or molecule of the substance.

Not every one of the particles of a substance have the exact same kinetic energy. At any given time, the kinetic energy of the particles deserve to be stood for by a distribution. Part atoms or molecules have actually a the majority of kinetic energy and also move an extremely fast. Other atoms or molecules have actually a small kinetic energy and move really slowly. The is the typical kinetic power of the particles the thermometers measure and also we document as the temperature.

One procedure that illustrates differing kinetic energies specifically well is evaporation. As you probably know, evaporation is a phase adjust where particles of a substance relocate from the liquid phase into the gas phase.

But have actually you ever before wondered just how a pond of water have the right to evaporate in ~ room temperature? store that in mind—we’ll come back to that inquiry in a bit.


When we think about a phase readjust from fluid to gas, we frequently think around adding thermal power to a fluid by heating it up. When we do, the molecules of the liquid relocate faster and spread contempt farther apart, till they acquire enough power to get rid of the attractions they have for other molecules that the liquid and enter the gas phase.

Think about this: If who asked friend to turn a beaker complete of water right into water vapor, what would certainly you do?

Being the excellent young scientist that you are, you could put that on a warm plate and also crank up the heat. Currently you deserve to kick back and relax until the hot plate transfers enough power to gain all the water molecules to change from the fluid phase come the gas phase. In much less science-y terms, you would boil the water.

Boiling is a special instance of a liquid-to-gas phase change that wake up at a particular temperature called the boil point, whereby the vapor push of the substance is same to one environment pressure. Cook is usually lugged out utilizing a consistent input of energy from one external resource (like a warm plate) to store the temperature constant.

The apparent conclusion is this: If girlfriend continuously include thermal power from a warm plate you can reason a phase readjust from liquid to gas.

But how can a puddle of water evaporate in ~ room temperature?

When water evaporates at room temperature, some fast-moving, extremely energetic molecules have enough energy to conquer the attractions the individual molecules have for one another and also enter the gas phase. As these high-energy molecules leave the fluid phase, the average power of the continuing to be liquid molecules is lowered, and also their temperature decreases. This liquid is in ~ a lower energy than that is surroundings, so it absorbs power from those surroundings. The cycle proceeds as the puddle progressively disappears.

Boiling is a faster process because the surroundings (the hot plate) warmth the liquid to a higher temperature where an ext molecules have actually high energy, therefore vaporization is faster. The hot plate is hotter 보다 the liquid, therefore thermal power transfer is fast enough to save the liquid temperature continuous at the cook temperature.

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Evaporation have the right to take location at any temperature because some of the molecules in a liquid—the ones at the greater end that the distribution—will constantly have enough energy to go into the gas phase. Chris

To sum up, temperature represents the typical kinetic power of the particles of substance. Yet it’s the spread of kinetic energies among the individual particles that defines why puddles dried up.