Lesson Video: Energy from Fossil Fuels Physics

In this lesson, we will learn how to describe the advantages and disadvantages of generating electricity by burning fossil fuels.


Video Transcript

In this video, we’re talking about energy from fossil fuels. Taken altogether, energy we derive from fossil fuels makes up about 85 percent of the global energy supply. In this lesson, we’ll learn what fossil fuels are, as well as advantages and disadvantages of this particular energy supply.

As we get started, one thing to make clear is that when we talk about getting energy from fossil fuels, we’re not talking about fossils themselves exactly. That’s because an intact fossil, well-preserved remains of an ancient plant or animal, would be far too precious to burn for energy. But it is true that fossil fuels come from ancient decomposed remains of organic matter. The process by which fossil fuels are developed goes like this.

Long, long ago, when plants and animals, initially alive at that time, died, their remains went into the ground and began to decompose. Over time, over the course of millions of years, the chemical composition of these remains began to change. Atoms of hydrogen began to attach to the carbon that was already part of this dead organic matter. When those attachments were made, energy rich bonds between carbon and hydrogen developed.

It’s since been discovered that there’s a way to harvest, or use, this energy. It’s by burning this material. Another word for that is combustion. Combustion breaks apart these bonds and releases the energy they store. This is what makes fossil fuels so useful as an energy source. We’ve seen so far that though fossil fuels aren’t fossils exactly, they do come from the remains of plants and animals. In general, there are three types of these fuels, natural gas, oil, another word for this is petroleum, and coal.

The primary use of energy that we derive from fossil fuels is in generating electricity. But there are other uses for these fuels as well. For example, we process oil, or petroleum, to create gasoline that our vehicles use to run. As we mentioned earlier, if we add up all the energy derived from the three fossil fuels, this amounts to the great majority of the energy used in the world. Knowing that fossil fuels are such a common energy source, let’s consider some of their advantages and disadvantages.

First off, among their advantages, fossil fuels generate large quantities of energy per unit mass. We could say they’re very energy rich or energy dense. Another advantage of these fuels is that they’re capable of providing power at any time. They’re not limited by weather conditions or day–night patterns or seasonal fluctuations. As long as we have some quantity of fossil fuels, we can burn it at any time to generate electricity day and night.

A third advantage is that a fossil fuel power plant, in particular a gas power station, is capable of responding quickly to changing energy needs. Recall that power stations are connected by a large electrical grid to energy consumers. Energy demands can rise and fall over time. And it’s important to be able to respond quickly to those changes. A power plant, or power station, fueled by natural gas is capable of starting up and reaching full production capacity in about 10 minutes time. This means that whenever more energy is required, a certain type of fossil fuel, natural gas, is capable of supplying that need quickly.

Along with these advantages, there are also some disadvantages to getting energy from fossil fuels. The first, and perhaps biggest, disadvantage of using fossil fuels is that when we burn them, energy isn’t the only product released. There are other unwanted byproducts of burning fossil fuels such as carbon dioxide, a greenhouse gas that, along with methane, helps to trap heat in Earth’s atmosphere. This has the effect of contributing to the overall warming of the Earth.

But it’s not only greenhouse gases like carbon dioxide that are released when fossil fuels are burned. Other pollution is released as well, including carbon monoxide, sulphur dioxide, which leads to acid rain, volatile organic compounds, and so on. These unwanted byproducts from burning fossil fuels are one of the main reasons, if not the main reason, for the search for other energy sources.

A second disadvantage of fossil fuels is that as a fuel source, they’re nonrenewable. Think back to how fossil fuels are created in the first place. That happened through the decay of organic remains over the course of millions of years. Now, it’s true that any organic matter decaying today will also lead to the creation of fossil fuels millions of years down the road.

But if we use up this fuel faster than it’s being produced, that means eventually we’ll run out. Unlike wind energy or solar energy, both of which are not depleted by our use of them, the more we use fossil fuels, the less we have. In this way, fossil fuels are a nonrenewable source of energy. Knowing all this about fossil fuels, let’s get a bit of practice now through an example exercise.

Which of the following are fossil fuels? Coal, uranium, oil, natural gas, plutonium.

Alright, to figure out which of these five options are and are not fossil fuels, we’ll want to recall a bit about how these fuels are generated. Fossil fuels come from decayed organic matter, including plants and animals. Over the course of millions of years, the carbon already present in these organisms joins up with hydrogen. And it’s the bonds between these two elements that store so much of the energy in fossil fuels.

Now, as we look down our list of five options, we see that two of them, uranium and plutonium, are pure atomic elements. In other words, we could look them up and find them on the periodic table of elements. This tells us that neither one of these choices contains any carbon or hydrogen atoms. Uranium is simply uranium, and plutonium is simply plutonium.

But if they don’t contain any bonds between hydrogen and carbon, that means they can’t be fossil fuels. After all, it’s those high-energy bonds that make fossil fuels what they are. This tells us we can cross off both uranium and plutonium from our list of options.

Now, the three remaining options, coal, oil, and natural gas, are formed through the process that we described, through the gradual decay of organic matter. For that reason, and because of their resulting chemical composition, all three of these are fossil fuels. And in fact, taken together, coal, oil, and natural gas make up all of the fossil fuels there are.

Let’s take a look now at a second example exercise.

In a gas-fired power station, natural gas is combusted with blank. The energy released from this reaction is used to heat water in a boiler to produce blank. This steam is used to drive blank, which are connected to blank. The electrical output of these generators is transferred to the national grid.

Now, our mission, should we choose to accept it, is to fill in the blanks in this statement. As we read the information that is given to us, we can see that this question is about a gas-fired power station and how it works. In our first sentence, we’re told that natural gas, the fuel for this kind of power station, is combusted with some other ingredient. Now, to figure out what this other ingredient is, we can think of combustion, burning, in general.

Say that we have a candle that’s burning. And then, we take a glass, turn it upside down, and then put the glass over the top of the candle. If we do that and keep the glass there, eventually the flame will die out, and the burning will stop. The reason this happens is because we’ve removed a necessary ingredient for combustion. It comes from the air around the candle. And that ingredient is oxygen. Oxygen is a necessary ingredient for combustion, or burning, to happen. So, we write that word in our first blank. That’s what natural gas is combusted with.

Our statement goes on to say that the energy released from this reaction is used to heat water in a boiler to produce blank. Alright, so, so far, what we have is natural gas combining with oxygen and being combusted. And now, we’re told that the energy released from this reaction is used to heat water in a boiler. Now, when water is heated enough to the point that it leaves its liquid phase, it becomes a gas. The name for that is steam. Our statement tells us that the water being heated is in a boiler. In other words, it’s the intention to transfer this water from being a liquid to being a gas. And, as we said, that gas is called steam. So, that’s what we’ll put in our second blank.

Now, the steam in the power station is typically produced in order to create pressure in a gigantic cylinder known as a turbine. Pushed by the high-energy steam, this turbine begins to rotate, or turn around its axis. This tells us how to fill in the third blank in our statement. The steam is used to drive turbines. It’s important to know, though, that rotating turbines by themselves don’t produce electricity. They have to be connected, typically by a rotating shaft, to a device called a generator.

When the turbine rotates, it causes the central portion of the generator to spin as well. When this component is rotating, the generator is able to produce electricity. So, then, generators are what are connected to turbines. And that word, generators, goes in our last blank.

Now, that all the blanks are filled in, let’s read our statement in its finished form. In a gas fired-power station, natural gas is combusted with oxygen. The energy released from this reaction is used to heat water in a boiler to produce steam. This steam is used to drive turbines, which are connected to generators. The electrical output of these generators is transferred to the national grid.

Let’s summarize now what we’ve learned about energy from fossil fuels. Starting off, in this lesson, we saw that fossil fuels are formed by decomposing organic material, that is, plants and animals, over millions of years. There are three types of fossil fuels, oil, also called petroleum, coal, and natural gas. And finally, we learned about the advantages and disadvantages of using fossil fuels for energy supply.

Advantages of fossil fuels include that, per unit mass, they produce lots of energy. They’re also capable of being used to produce power at any time day or night. And along with this, gas-fired power stations in particular are capable of quickly responding to increased energy needs.

On the disadvantages side, burning fossil fuels releases carbon dioxide, a greenhouse gas, as well as other types of pollution. And another disadvantage is that fossil fuels are a nonrenewable fuel source. This is an overview of what fossil fuels are, as well as the pros and cons of using them for energy.

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