The Laws of Thermodynamics

Core Concepts

There are three fundamental laws of thermodynamics, which deal with the movement and transfer of energy. Let’s learn about them in this tutorial. We will discuss the first law of thermodynamics, the second law of thermodynamics, and the third law of thermodynamics.

Laws of Thermodyamics Made Easy

What is Thermodynamics?

Thermodynamics is a branch of physics that studies the relationship between heat, work, and energy. It is the way in which heat can be converted into work, and the effect of this conversion on the properties of matter.

In simple terms, thermodynamics deals with how heat behaves and how it can be used to do work. For example, if you rub your hands together, you create heat by converting the energy of your movements into heat. The heat then warms your hands.

A good way to understand thermodynamics is to think about the four laws of thermodynamics. These laws describe the basic principles that govern the behavior of heat and energy.

Thermodynamics is a fascinating and important field of study that has many practical applications in the real world. It helps us understand the behavior of heat and energy, and allows us to design systems that can efficiently convert heat into work.

First Law of Thermodynamics Simply Explained

The first law of thermodynamics is a basic principle of physics that describes the relationship between energy and heat. It states that energy cannot be created or destroyed, only transferred or converted from one form to another. In other words, the total amount of energy in a system remains constant, even as that energy is transferred or converted.

A simple way to understand the first law of thermodynamics is to think about a closed system, such as a sealed container with a gas inside. If heat is added to the gas, the temperature of the gas will increase. The increased temperature causes the gas to expand, doing work on the surroundings. This increase in the gas’s temperature and pressure is due to the transfer of heat from the surroundings to the gas. The first law of thermodynamics tells us that the total amount of energy in the system (the gas and its surroundings) remains constant, even as the heat is transferred from the surroundings to the gas.

In other words, the first law of thermodynamics can be thought of as a statement of the conservation of energy. It tells us that energy is always conserved, even as it is transferred or converted from one form to another. This principle has many important applications in various fields, including thermodynamics, engineering, and chemistry.

Second Law of Thermodynamics Simply Explained

The second law of thermodynamics is a basic principle of physics that describes the behavior of heat and the direction in which heat will flow. It states that heat will always flow from a hotter object to a colder one, and that this process is irreversible.

In simple terms, the second law of thermodynamics tells us that heat always moves from hotter objects to colder ones. It also says that it is impossible to convert heat into work with 100% efficiency. For example, if you have a cup of hot coffee and a cup of cold water, the heat from the coffee will naturally flow into the cold water, causing the coffee to cool down and the water to warm up. This process is irreversible, meaning that you cannot reverse it by simply stirring the cups or mixing the contents.

A good way to understand the second law of thermodynamics is to think about the concept of entropy. Entropy is a measure of the disorder or randomness in a system. The second law of thermodynamics tells us that the entropy of a closed system will always increase over time. In other words, the natural tendency of any system is to become more disordered and random.

For example, if you have a sealed container with a gas inside, the gas molecules will move around randomly and collide with each other. Over time, the gas will become more and more disordered, and the entropy of the system will increase. This increase in entropy is a result of the second law of thermodynamics, which tells us that heat will always flow from hotter objects to colder ones, and that this process is irreversible.

Overall, the second law of thermodynamics is a fundamental principle of physics. The las has many important applications in various fields, including thermodynamics, engineering, and chemistry. It helps us understand the behavior of heat and the direction in which it will flow, and allows us to design systems that can efficiently convert heat into work.

Third Law of Thermodynamics Simply Explained

The third law of thermodynamics is a fundamental principle of physics that describes the behavior of entropy at very low temperatures. It states that as the temperature of a system approaches absolute zero, the entropy of the system approaches a constant minimum value.

In simple terms, the third law of thermodynamics tells us that as the temperature of a system gets closer and closer to absolute zero, the entropy of the system will approach a constant minimum value. Absolute zero is the lowest possible temperature, and is equal to -273.15 degrees Celsius or -459.67 degrees Fahrenheit. At this temperature, the particles in a system stop moving and the system reaches a state of complete disorder and randomness.

A good way to understand the third law of thermodynamics is to think about the concept of entropy. Entropy is a measure of the disorder or randomness in a system. The third law of thermodynamics tells us that as the temperature of a system approaches absolute zero, the entropy of the system will approach a constant minimum value.

For example, if you have a sealed container with a gas inside, the gas molecules will move around randomly and collide with each other. As the temperature of the gas decreases, the gas molecules move slower and slower. Because the particles are moving slower, the entropy of the system will decrease. Eventually, as the temperature approaches absolute zero, the gas molecules will stop moving altogether and the entropy of the system will reach a constant minimum value.

Overall, the third law of thermodynamics is a fundamental principle of physics that has many important applications in various fields, including thermodynamics, engineering, and chemistry. It helps us understand the behavior of entropy at very low temperatures. It also allows us to predict the behavior of systems as they approach absolute zero.

What is a System?

Before delving into the three laws of thermodynamics, it is important to understand the concept of a system and surroundings.

Thermodynamics becomes much easier when a clear boundary is drawn. Anything inside the boundary is called the “system,” and anything outside the boundary is called the “surroundings.” Once the boundary diagram is drawn, the movement and transfer of energy can be characterized by the flow across system boundaries.

The term “universe” is all-encompassing. In other words, refers to both the system and the surroundings.

Types of Systems

Based on the type of law and exchanges, there exist three types of systems: open systems, closed systems, and isolated systems. Firstly, in an open system, there is an exchange of both matter and energy. Next, in a closed system, there is no exchange of matter but some exchange of energy. Finally, in an open system, there is an exchange of both matter and energy. Understanding the differences between these systems is crucial to understanding the laws of thermodynamics.

What is thermodynamics?

Thermodynamics is the branch of physics that deals with the relationships between work, heat, temperature, and energy. Additionally, thermodynamics looks at the science of how thermal energy is converted between forms of energy and how thermal energy affects matter. Thermal energy is defined as as the energy that comes from heat.

Laws of Thermodynamics: The First

The First Law of Thermodynamics is summarized by: energy cannot be created or destroyed. In other words, total energy of the universe must remain constant, or conserved.

∆U_universe = 0

However, it is important to note that energy takes different forms. Another way of restating the first law, is to say that the change in energy is equal to the heat flow across the system (Q) plus the work done on the system or by the system (W). This equation is shown below.

∆E_system = Q + W

∂E = ∂Q + ∂W in differential form

So, heat and work are are two processes which can change the internal energy of a system. If heat flows into the system, Q is positive. This means that heat is gained by the system. And the same magnitude of heat is lost by the surroundings (endothermic reaction). If heat flows out of the system, Q is negative. This means that heat lost by the system is equal in magnitude to the heat gained by the surroundings (exothermic reaction).

The same idea is for work. If the surroundings does work on the system, then work is positive. If the system does work on its surroundings then work is negative. Either way, total energy remains conserved. Below summarizes this concept.

Laws of Thermodynamics: The Second

The Second Law of Thermodynamics deals with entropy and, to an extent, limits the first law. According to the second law, entropy of a spontaneous process must increase.Aand the the entropy of the universe, as an isolated system, must always increase. This is because, achieving maximum entropy means that a system is at equilibrium. All systems are always trying to reach equilibrium, and increase their Gibbs Free Energy.

∆S_universe > 0

Processes can allow entropy of a system to decrease, but in that case, entropy of the surroundings will increase. This does not break the second law.

∆S_universe = ∆S_system + ∆S_surroundings

Spontaneous Processes

A spontaneous process is one that occurs without any input. According to the second law of thermodynamics, in a spontaneous process, entropy must increase. You can understand entropy as either reaching equilibrium, or as increasing disorder of a system.

An example of a spontaneous process is heat moving from a hot to a cold body. Heat will naturally move from hot to cold without any external input. This movement is because the overall system is trying to reach an even temperature.

graphic depicting the second of the three laws of thermodynamics

As heat leaves the hot system system, its own entropy decreases. And then as it enters the cold system, its entropy increases. This is a spontaneous process.

On the other hand, a non-spontaneous process is one where entropy decreases.

Note that spontaneity does not refer to speed! It refers to a process that naturally occurs without interference. A spontaneous process can actual have a very slow reaction rate.

Laws of Thermodynamics: The Third

The Third Law of Thermodynamics holds that the entropy of a system nears a constant value as its temperature approaches absolute zero. This law generally applies to a pure material in a perfectly crystalline structure, because its minimal energy allows to approach zero entropy. If the crystal isn’t perfect or if not at 0 K, then there will thermal motion that will lead to disorder. Tutorials