Applying the First Law of Thermodynamics to Reactions & Processes

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  • 0:01 The Law of Energy Conservation
  • 1:07 What Is Energy?
  • 3:45 Conversions Between…
  • 5:59 Energy and Matter
  • 6:54 Lesson Summary
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Lesson Transcript
Instructor: Nicola McDougal

Nicky has taught a variety of chemistry courses at college level. Nicky has a PhD in Physical Chemistry.

In this lesson, we'll see how different forms of energy are related. We'll learn and apply the laws of conservation of mass and energy to chemical reactions, physical processes, nuclear reactions, and biological processes. A quiz will test your new knowledge.

The Law of Energy Conservation

Meet George. It is early morning, and he is doing some of his favorite things. He loves to run after his ball, he particularly loves to eat his breakfast, and he loves to watch TV. All of these activities have something very important in common. They are all changing one form of energy into another. George chasing after his ball converts potential energy to kinetic energy. George's body converts chemical energy in food to mechanical energy. And, the TV converts electrical energy to electromagnetic energy. And, all of these activities show us that energy is conserved.

The Law of Conservation of Energy is also known as the First Law of Thermodynamics. It tells us that energy cannot be created or destroyed. In our examples with George, we saw that the energy may have changed type, but the total amount of energy is the same before and after any process.

What Is Energy?

Before we start looking more at the conversion of energy, let's briefly remind ourselves what energy is. Energy can simply be defined as the ability to do work or cause change. There are two general kinds of energy. The first type is kinetic energy, which is the energy of motion. The kinetic energy of an object depends on both its mass and its velocity, or speed.

To help understand this, let's think about George running with his friend Ellie. They are both running at the same speed at around 6 mph. But you can see Ellie is a lot smaller than George; in scientific terms we would say she has less mass. Which dog do you think is doing the most work and has the highest kinetic energy? You would be right if you said George. George has more mass and has to do more work to run at the same speed as Ellie. The more work that is done, the higher the kinetic energy.

The second general kind of energy is potential energy. This is the energy of position. There are two types of potential energy. Objects that can be stretched possess elastic potential energy. Objects at a height possess gravitational potential energy. Potential energy is often thought of as stored energy ready to be used later. This type of energy has the potential to do work.

George and Ellie are very excited because the ball is just about to be thrown for them. You can see the ball above this person's head. It has gravitational potential energy. We say the ball has potential energy at this point because it is ready to do work. As soon as the ball is released, the potential energy is transferred into kinetic energy, and the ball moves through the air.

You may have heard of other types of energy. Both kinetic and potential energy can have a variety of different forms. The different forms of energy include mechanical energy, thermal energy (or heat), chemical energy, electrical energy, electromagnetic energy, and nuclear energy.

Conversions Between Forms of Energy

Now that we know about the different types of energy, let's think about ways they are converted. We come across energy conversions all the time. We saw right at the beginning of the lesson how George's activities involved different energy conversions. Recall we learned that George chasing after his ball converts potential energy to kinetic energy. We also learned that George's body converts chemical energy in food to mechanical energy. And finally, we learned that the TV converts electrical energy to electromagnetic energy. The important point is that energy is always converted from one form to another.

Let's now think about one more example of energy conversion.

George is an exceptional dog because he is about to ski down a mountain. We can think about the different energy conversions as he goes. Right now George just sits on his skis at the top of the mountain. He has gravitational potential energy. His position on the top of the mountain gives him the potential to do work. As George pushes off down the mountain, the potential energy is converted to kinetic energy because he is moving. The faster he goes, the more kinetic energy he has.

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