Laws of Thermodynamics - Online Tutor, Practice Problems & Exam Prep

The first law of thermodynamics states that energy can be transferred and transformed but cannot be created or destroyed, emphasizing the principle of conservation of energy. In contrast, the second law highlights that energy conversions are never 100% efficient, as some energy is lost as heat, increasing universal entropy. Entropy measures disorder, with systems naturally progressing towards higher entropy unless energy is input to create order. Understanding these laws is crucial for grasping energy dynamics in biological systems, including cellular respiration and photosynthesis.

First Law of Thermodynamics

So now that we know that thermodynamics is the study of energy and energy transfers, in this video we're going to introduce the First Law of Thermodynamics. And so the First Law of Thermodynamics basically says that energy can be transferred from one substance to another substance, and energy can also be transformed from one form into another form. But energy cannot be created or destroyed. And so this is why the first law of thermodynamics is also known as the principle of conservation of energy. And this is, again, because the total amount of energy in the universe is conserved, meaning that it does not change.

And so the total amount of energy before a process is going to be equal to the total amount of energy after a process, since energy is not created or destroyed. Again, energy can be transferred from one substance to another and it can be transformed from one version of energy into a different version of energy such as, kinetic energy into potential energy and vice versa. But again, energy cannot be created or destroyed, and this is basically what the first law of thermodynamics says. So let's take a look at our image down below to get a better feel for this first law of thermodynamics. And so notice that in this image over here, we're showing you a plant cell over here on the far left.

And zooming in here, you can see that we have our plant. And inside of the plant, we have this chloroplast, which recall performs photosynthesis. And then over here on the right-hand side, we're showing you, an animal cell, right here. And we're zooming into this little bunny rabbit which is an animal and you can see that the, the bunny here we're zooming into this mitochondria here which performs cellular respiration. And so also notice that we have the sun here.

And the sun is really where most of the energy of life is going to originate from. And so the sun's energy, its solar energy, can be captured by photosynthetic organisms such as plants that perform photosynthesis. And photosynthesis is capable of transforming the solar energy into the chemical energy of glucose. It also creates some oxygen in the process. But what you can see is that energy is being transferred from the sun and being transferred from the sun to create a different type of energy, chemical energy here.

And so what we're saying is that energy is transferred, but once again it cannot be created or destroyed. Now, the animal cell over here, the little bunny rabbit, is able to eat the leaves and eat the plant, and when it does that it can obtain the energy of the glucose and then it can use the energy of the glucose to create a different type of energy, ATP, energy that can be used by the cell. And so ultimately, what we're seeing is that energy can originate from the sun. It can be converted into the chemical energy of glucose. It can be transferred to other organisms such as little bunny rabbits that can eat them.

And then, of course, the bunny rabbits, when the bunny rabbits pass away and also when they conduct cellular respiration, they can transfer their nutrients back to plants. And so they're able to create carbon dioxide and water that photosynthesis is able to take advantage of. And so here what we're saying is that the first law of thermodynamics is that energy can be transferred and transformed into different versions, but once again it cannot be created or destroyed. And so you can see the energy here is flowing in this direction and it just cycles between different forms, but it's never created or destroyed. And so this here concludes our brief introduction to the first law of thermodynamics, and we'll be able to get a little bit of practice as we move forward in our course.

So I'll see you all in our next video.

Which of the following statements describes the first law of thermodynamics?

• A. Energy cannot be created or destroyed.
• B. Energy cannot be transferred or transformed.
• C. Also called The Principle of Creation of Energy.
• D. Energy can be destroyed.

Entropy

Now before we get into the second law of thermodynamics, it's first important to understand the idea behind this term called entropy. Entropy is defined as a measure of disorder, or in other words, a measure of randomness. The greater the disorder is, the higher the entropy will be. Let's take a look at this image down below right here to get a better understanding of entropy. Notice over here on the left-hand side, we have this pool table, and the billiard balls here that you see are very, very highly organized and very, very ordered.

However, notice over here on the right-hand side, this pool table has the same billiard balls here that are scattered throughout the entire table, and so they're not very highly ordered. They're not very highly organized. Instead, they're pretty greatly disordered over here. And so because they are more disordered over here, the greater the disorder, the higher the entropy. And so this system over here is going to have higher entropy.

And, of course, this system over here that is highly ordered and not very disordered, it's going to have low entropy. And so the lower the entropy, the more organized and the more ordered it is, whereas the higher the entropy, the more disordered it is and the more unorganized it is. Now, the natural tendency of reactions is to move the universe towards a state of maximum entropy or maximum disorder. And so the natural tendency of the universe is for things to go from a state of order, towards a state of disorder, a state of higher entropy. This represents the natural tendency of reactions.

However, reactions can decrease the entropy of a system, essentially going backwards in this direction, with an energy input. As you can see down below, with an energy input, reactions can become more ordered. And so this is really what life is capable of doing. Living organisms are capable of inputting energy so that they can create order in their systems. But the natural tendency of the universe is to go from a state of low entropy towards a state of higher entropy.

And so the reactions are going to have this tendency to move towards the state of maximum entropy or maximum disorder. And so this is an idea that you would get to learn a lot more about in a chemistry course. But here in our biology course, this concludes our introduction to entropy and we'll be able to apply entropy in the second law of thermodynamics which we'll cover in our next video. So I'll see you all there.

Which of the following images has less entropy?

• A. Image A has less entropy.
• B. Image B has less entropy.

Second Law of Thermodynamics

In this video, we're going to introduce the second law of thermodynamics. The second law of thermodynamics can actually be stated in many different ways, and it's possible that your professor or your textbook might state the second law of thermodynamics in a different way. But really, all the second law of thermodynamics is trying to say is that 100% efficient energy conversion is impossible since heat energy is going to be lost with every energy transfer, and this is going to lead to the increase of the overall universal entropy. Heat is defined as a form of kinetic energy that is transferred between two objects with different temperatures.

Let's take a look at our example below at the second law of thermodynamics to get a better understanding of it. Notice that we're showing you a similar process to our last lesson video on the first law of thermodynamics. You can see that the sun is the energy provider where most of the energy originates for life. The energy transfer here, from solar energy to plants, is going to be accompanied by a loss of heat. With every energy transfer, some of the energy is lost as heat.

There is not a 100% efficient energy conversion. Some of the energy is lost as heat, and that heat is not a usable form of energy by the organism. The same goes for when an organism eats the leaf; the energy transfer here is going to be accompanied by a loss of heat. The same is true when the fox eats the mouse. There's going to be a transfer of energy, but some of it will be lost in the form of heat.

This heat that is being lost with every energy transfer is going to lead to the increase in the entropy of the universe. The entropy of the universe is always increasing with every energy transfer. This is really what the second law of thermodynamics is referring to: the increasing of universal entropy with every energy transfer. This concludes our introduction to the second law of thermodynamics and we'll be able to apply some of the concepts that we've learned here as we move forward in our course. I'll see you all in our next video.

When chemical, transport, or mechanical work is done by an organism, what happens to the heat generated?

• A. It is used to power yet more cellular work in the surroundings.
• B. It is captured to store energy as more heat in the system.
• C. It is used to generate ADP.
• D. It is lost to the environment.

Which of the following statements is true regarding how energy moves up the food chain?

• A. All of the energy is not transferred from producer to consumer because some of the energy is destroyed.
• B. All of the energy is transfer from producer to consumer.
• C. All of the energy is not transferred from producer to consume because some of the energy is lost as heat.
• D. None of the above.

Here’s what students ask on this topic:

What is the First Law of Thermodynamics and how does it apply to biological systems?

The First Law of Thermodynamics, also known as the principle of conservation of energy, states that energy can be transferred and transformed but cannot be created or destroyed. In biological systems, this law is evident in processes like photosynthesis and cellular respiration. For example, plants convert solar energy into chemical energy stored in glucose during photosynthesis. When animals consume plants, they transform this chemical energy into ATP, which cells use for various functions. Throughout these processes, the total amount of energy remains constant, merely changing forms but never being created or destroyed.

What is entropy and how does it relate to the Second Law of Thermodynamics?

Entropy is a measure of disorder or randomness in a system. The Second Law of Thermodynamics states that energy conversions are never 100% efficient, as some energy is always lost as heat, leading to an increase in universal entropy. This means that natural processes tend to move towards a state of higher disorder. For instance, when energy is transferred from the sun to plants and then to animals, some energy is lost as heat at each step, increasing the overall entropy of the universe.

How does the Second Law of Thermodynamics explain the inefficiency of energy transfers in biological systems?

The Second Law of Thermodynamics explains that energy transfers are never 100% efficient because some energy is always lost as heat. In biological systems, this inefficiency is seen in processes like cellular respiration and photosynthesis. For example, when plants convert solar energy into chemical energy, some energy is lost as heat. Similarly, when animals convert the chemical energy in food into ATP, more energy is lost as heat. This loss of energy as heat increases the entropy of the universe, making 100% efficient energy conversion impossible.

Why is the concept of entropy important in understanding biological processes?

Entropy is crucial for understanding biological processes because it explains the natural tendency of systems to move towards disorder. In biological systems, maintaining order requires a constant input of energy. For example, living organisms must consume food to obtain energy, which they use to maintain cellular functions and organization. Without this energy input, biological systems would move towards higher entropy, leading to disorder and ultimately, the cessation of life. Thus, understanding entropy helps explain why energy is essential for life and how organisms manage energy to sustain order.

How do the laws of thermodynamics apply to cellular respiration and photosynthesis?

The laws of thermodynamics are fundamental to understanding cellular respiration and photosynthesis. The First Law of Thermodynamics states that energy can be transferred and transformed but not created or destroyed. In photosynthesis, plants convert solar energy into chemical energy stored in glucose. In cellular respiration, organisms convert this chemical energy into ATP, which cells use for various functions. The Second Law of Thermodynamics states that energy transfers are never 100% efficient, as some energy is lost as heat. This inefficiency is evident in both photosynthesis and cellular respiration, where energy is lost as heat at each step, increasing the entropy of the universe.