Video: Understanding Heating

Heating a substance increases the _ of the substance, which leads to a _ or a _.

02:38

Video Transcript

Heating a substance increases the blank of the substance, which leads to a blank or a blank.

In this question what we wanna do is fill in the blanks. As far as what’s going on in this situation, we know that we’re heating some substance. So let’s say we have our substance right here. And we’re applying heat to it, say by putting a Bunsen burner beneath it. However we heat our substance, we know that this step involves transferring heat energy into this material. Before we say what effect this transfer of heat has on the substance, we can simply observe that it’s absorbing heat, that it’s gaining energy this way.

Here’s how we can put this. We can say that our substance started out with some internal energy. We’ll call it 𝐸 sub 𝑖. That internal energy is simply the measure of the total energy that our substance possesses in and of itself. Then when we heat our substance, we’re adding energy to it. At the most basic level, this means that the internal energy of our substance will go up. We know that this change in internal energy will take place regardless of how the substance responds to the change. So we figured out what goes in our first blank in the sentence. When we heat our substance, we increase its internal energy.

The next two blanks on our sentence have to do with what this increase in internal energy creates, what it leads to. Here, it can be helpful to think of a specific type of substance rather than a substance in general. Let’s say that this substance we have here is a piece of ice. As we apply heat to the ice, we give it energy and we raise its internal energy level. How can the ice respond to this increase?

Well, there are one of two things it could do. Number one, the temperature of the ice could go up. That’s a natural outcome of an object being heated. Or, and we’ve experienced this as well, the ice could melt. That is, it could become a liquid. Let’s imagine that this chunk of ice has an initial temperature. We’ll call it 𝑇 sub 𝑖 of negative 10 degrees Celsius. We know that ice melts at zero degrees Celsius. So if we put heat into this chunk of ice, it wouldn’t be able to melt right away because its temperature is still too low. That heat then would increase the internal energy with the effect of raising the temperature of the ice.

Eventually though, when the temperature of that ice got up to zero degrees Celsius, then it will be capable of melting. It will be capable of going through a change of state. Going back now to our general scenario — where we have some substance, we don’t know what it is, being heated — we can see that this increase in internal energy that results from the heating could lead to one of two things. It could lead to a change in temperature in our substance. Or it could lead to a change of state, like we imagined with a chunk of ice melting to become liquid water. And with that figured out, we’ve now filled in the blanks in this sentence.

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