Thermal Conductivity | Best Chemistry Review

Heat Transfer at the Molecular Level

Heat Transfer at the Molecular Level

Today, we’re going to briefly overview heat transfer on the molecular level, or what is known as thermal conduction. This is the transfer of heat from the collision of molecules or the interaction of atoms within a substance (a solid, a liquid, or a gas).

We’re going to, for example purposes today, use solids to talk about the concept of heat transfer or thermal conduction. Basically, what happens is when an object is heated (heat is applied), in this case we have a frying pan sitting on a stovetop, heat is being transferred into the frying pan.

Here we’ll just say it’s a cast iron skillet, so it’s all metal. At first, the handle out here is cool. It can be picked up with the bare hands. No problem. The heat that is coming here up into the bottom of the skillet is going to be transferred throughout the entire body.

As these atoms interact with the other atoms over here, as the molecules interact, heat is transferred. The collisions transfer heat and energy. That heat and energy then continues to be transferred until it spreads throughout the entire object.

If the heat is taken away, what you will find then is that the heat will transfer throughout, the hotter areas will get cooler, the cooler air will get hot until you reach a state of equilibrium, where, basically, there’s a uniform temperature.

The whole idea here of heat transfer at the molecular level is when heat is applied, the molecules in the object, in this case the frying pan, are agitated. As they move and collide with the other molecules and atoms, energy and heat are transferred.

Because of that, what is ordinarily a cool spot out here will get warmer. The heat will transfer throughout the object because of those interactions. Another example of this, showing that the temperature, the heat, is transferred but no transfer of actual matter takes place is when you place a hot coffee cup on top of a desk or a table.

The liquid inside (the hot coffee inside the coffee cup) doesn’t actually exchange molecules. The coffee and the cup don’t interchange, but the heat is transferred to the cup and from the cup to the desktop.

When you lift the cup up, there’s usually some sort of condensation underneath it or you can put your hand on the surface and suddenly it feels warm. This is because there has been thermal conduction, or transfer of heat, from one to the other.

The basic idea is that heat transfers, not actual matter transfers, and it’s due to the interaction of the molecules or atoms as they are heated, they’re agitated, they bump into the other ones. This collision transfers energy and, therefore, heat and it spreads throughout.

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Last updated: 10/18/2018


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