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.
