(a) What phase change is represented by the "heat of fusion" of a substance? (b) Is the heat of

(a) What phase change is represented by the "heat of fusion"...

Key Concepts

Heat of Fusion

The heat of fusion is the amount of energy required to change a substance from a solid to a liquid at its melting point, without changing its temperature. This process is endothermic, meaning it involves the absorption of energy.

Endothermic Process

An endothermic process is one that absorbs heat from the surroundings. In the context of phase changes, melting (fusion) is endothermic because the process requires an input of energy to overcome the forces holding the solid together.

Phase Transition

A phase transition is the process in which a substance changes from one state of matter to another, such as from solid to liquid or liquid to gas. These transitions occur when external conditions like temperature or pressure change, and they are characterized by latent heat, which is the energy absorbed or released during the change.

Latent Heat

Latent heat is the energy absorbed or released by a substance during a phase change without causing a change in temperature. This energy is involved in overcoming intermolecular forces during melting, freezing, vaporization, or condensation.

Heat of Vaporization

The heat of vaporization refers to the energy needed to convert a liquid into a gas at its boiling point, again without a change in temperature. Typically, the heat of vaporization is greater than the heat of fusion because more energy is required to completely overcome the intermolecular forces in liquids compared to solids.

Transcript

00:01 All right, in question 35, we're looking at the interaction between a liquid and a flat surface.

00:07 And so we're looking at the difference between cohesion, where cohesion is the attraction of the particles for each other, and adhesion, which is the attraction for the liquid particles to the surface.

00:22 So we're looking at the difference between cohesion and adhesion.

00:31 So again, this is between the...

00:35 The liquid particles between themselves.

00:43 And this one is between the liquid and the surface that it's on.

00:53 All right, so in part a, they ask us, in which of these diagrams, one or two, do the adhesive forces between the surface and the liquid exceed the cohesive forces within the liquid? so we want to see which one's the adhesive is great.

01:15 Raider.

01:18 So i'm going to put up the first.

01:22 In this one we've got a beaded droplet.

01:26 And so this has very strong cohesive forces because the forces that are holding all these guys inward attracted to each other is what's causing this to beat up.

01:35 So in this one we have high cohesive forces.

01:44 Figure two, we have our surface and the water is or the liquid is just kind of in a little puddle right there.

01:53 And so in this one, the liquid has a lot more attraction for the surface, because it's spreading out along the surface instead of beating up on itself.

02:02 So this one has high adhesion.

02:08 All right...

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