Laws of Thermodynamics: Study with Video Lessons, Practice Problems & Examples

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 introduces entropy, a measure of disorder, indicating that energy transfers are never 100% efficient, leading to increased universal entropy. Living organisms can input energy to create order, but the natural tendency is towards greater disorder. Understanding these laws is crucial for grasping energy dynamics in biological systems, including processes like photosynthesis and cellular respiration.

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, 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 bunny here we're zooming into this mitochondria here which performs cellular respiration. 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 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 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 nutrient over 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.

• 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, the higher the entropy will be. Let's take a look at this image below to get a better understanding of entropy. Notice on the left-hand side we have this pool table, and the billiard balls here are very highly organized and very ordered. However, on the right-hand side, the same billiard balls are scattered throughout the entire table. They are not highly ordered. Instead, they are greatly disordered. Because of this greater disorder, the entropy is higher. This system over here is going to have higher entropy. And, of course, this system that is highly ordered is going to have low entropy. The lower the entropy, the more organized and ordered it is, whereas the higher the entropy, the more disordered and unorganized it is.

The natural tendency of reactions is to move the universe towards a state of maximum entropy or maximum disorder. The natural tendency of the universe is for things to go from a state of order to 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 backward in this direction, with an energy input. You can see that with an energy input, reactions can become more ordered. This is what life is capable of doing. Living organisms input energy to 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. The reactions will have the tendency to move towards the state of maximum entropy or maximum disorder. 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. We will 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.

• 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. It's possible that your professor or your textbook might state the second law of thermodynamics differently. 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. 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 really going to be 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. This heat is not going to be a usable form of energy by the organism.

The same goes for when an organism might eat the leaf. The energy transfer here is going to be accompanied by a loss of heat. The same goes when the fox eats the mouse. There's going to be a transfer of energy, but some of the energy is going to 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 going to be increasing with every energy transfer. This here is really what the second law of thermodynamics is referring to, the increasing of universal entropy with every energy transfer.

This here 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. So 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.

• 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.

• 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?

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. This means the total amount of energy in the universe remains constant. For example, in biological systems, solar energy from the sun is converted into chemical energy through photosynthesis in plants. This chemical energy can then be transferred to animals when they consume plants, and further transformed into ATP during cellular respiration. Despite these transformations, the total energy remains conserved.

How does the second law of thermodynamics relate to entropy?

The second law of thermodynamics states that energy conversions are never 100% efficient because some energy is always lost as heat, which increases the entropy of the universe. Entropy is a measure of disorder or randomness. Natural processes tend to move towards higher entropy, meaning they become more disordered over time. For instance, when energy is transferred from the sun to plants and then to animals, some energy is lost as heat at each step, contributing to the overall increase in universal entropy.

What is entropy in the context of thermodynamics?

In thermodynamics, entropy is a measure of disorder or randomness in a system. A highly ordered system has low entropy, while a highly disordered system has high entropy. The natural tendency of the universe is to move towards a state of maximum entropy. For example, a neatly arranged set of billiard balls has low entropy, whereas scattered billiard balls have high entropy. Living organisms can decrease their internal entropy by inputting energy, thus creating order within their systems, but the overall entropy of the universe still increases.

Why is 100% efficient energy conversion impossible according to the second law of thermodynamics?

According to the second law of thermodynamics, 100% efficient energy conversion is impossible because some energy is always lost as heat during energy transfers. This heat energy is not usable by the organism and contributes to the increase in the entropy of the universe. For example, when plants convert solar energy into chemical energy, or when animals convert chemical energy into ATP, some energy is inevitably lost as heat, making perfect efficiency unattainable.

How do living organisms manage to decrease entropy within their systems?

Living organisms manage to decrease entropy within their systems by inputting energy. This energy input allows them to create order and maintain low entropy internally, despite the natural tendency of the universe to move towards higher entropy. For example, plants use solar energy to synthesize glucose during photosynthesis, creating an ordered structure from simpler molecules. Similarly, animals use the energy from food to build and maintain complex cellular structures, thus decreasing their internal entropy.