How to Learn Thermodynamics: Basic Concepts and Foundations

Co-authored by Eric McClure

Last Updated: August 25, 2021 References

Thermodynamics is the study of relationships between heat and other forms of energy. It’s technically a branch of physics, and it has reputation as one of the most difficult subjects for university students. While it’s true that thermodynamics can be pretty confusing, there’s no reason you can’t succeed if you’re a diligent student! With a little hard work and a razor-sharp focus in class, you’ll be on the right track to mastering this interesting subject.

Question 1 of 7:

Is thermodynamics hard to learn?

It is fairly difficult for a lot of people, but by no means impossible. The concepts in thermodynamics tend to be fairly complex, and there’s a good amount of elaborate math involved. As a result, it can be kind of hard to keep up if you lose track of how the math relates to the concepts and vice versa. The good news is that students who focus in class are scientifically proven to do better in this subject!^{[1]
X
Research source}
- There are also many students out there who find thermodynamics easy compared to fluid dynamics, organic chemistry, or calculus. Difficulty is relative, so if you have a strong background in science and math, there’s no reason to assume thermodynamics will be especially challenging.
- Many students find the definitions themselves kind of hard to follow. For example, internal energy and internal heat seem like they’d be the same thing, but they’re actually two totally different things.^{[2]
  X
  Research source}

Question 2 of 7:

How can I learn thermodynamics easily?

Take algebra, differential equations, and physics first. You may also benefit by taking some chemistry classes before you jump into thermodynamics.^{[3]
X
Research source} There’s a lot of complex math in thermodynamics, so knowing how to work through differential equations and high-level algebra will dramatically help.^{[4]
X
Research source}
- Remember, even if you don’t think you’re ready, the class will be much easier for you if you’re focused and attend every lecture!^{[5]
  X
  Research source}
- A lot of universities require you to take physics, differential equations, algebra, and organic chemistry before you’re allowed to take thermodynamics.^{[6]
  X
  Research source}

Question 3 of 7:

What is the first law of thermodynamics?

The first law basically says that energy cannot be created or destroyed. Energy can move or change its form, but it can’t appear out of thin air or be completely erased. This law is often expressed by the equation E2 - E1 = Q – W, where the internal energy of one system (E2) minus the internal energy of a second system (E1) is equal to the transfer of heat (Q) minus work (W).^{[7]
X
Research source}
- There’s actually a law that comes before the first law (the first law was discovered first). It’s known as the “zeroth” law. It states that when two objects are in thermodynamic equilibrium with a third object, then the two objects are also in equilibrium with one another.^{[8]
  X
  Research source}

Question 4 of 7:

What is the second law of thermodynamics?

The second law deals with entropy and the movement of heat. Essentially, if you have a hot object and a cold object next to one another, the heat will transfer from the hot object to the cold one. In fact, the second law states that it can’t work the other way.^{[9]
X
Research source} The formula is expressed as ΔS = ΔQ/T, where the change of Q (heat) divided by T (temperature) is equal to the change of entropy (ΔS) in a system.^{[10]
X
Research source}
- Entropy is a key concept in thermodynamics. Basically, entropy refers to the amount of energy that's unavailable to do work. A lot of concepts in thermodynamics rely on an understanding of entropy. You’ll learn a lot about this early on in class.

Question 5 of 7:

What is the third law of thermodynamics?

The third law states that a pure crystal with no heat has no entropy. This seems a little random, but it basically boils down to this: if there is no heat, no heat can escape. So, if you have an object with no internal energy and there’s no temperature, there’s no entropy.^{[11]
X
Research source} There is no formula for the third law of thermodynamics.^{[12]
X
Research source}
- Just think of the third law like this: heat has a tendency to leave if a system isn’t closed. If there’s no heat, there’s no transfer. It seems kind of obvious, but it’s an essential law when it comes to the behavior of heat and entropy.

Question 6 of 7:

What are the basic concepts of thermodynamics?

You’ll learn a lot about energy, mass, and heat. Thermodynamics is all about measuring and understanding how heat and other forms of energy interact with one another. So concepts like energy conversion, molecule behavior, and kinetic/potential energy are key. Entropy is another huge concept. You’ll also learn differences between open and closed systems, which changes how heat and energy functions.^{[13]
X
Research source}
- Any decent thermodynamics professor will cover the key concepts before they get into the relevant math. Be a diligent note taker in class and ask questions when your teacher is covering the concepts and you’ll be fine!

Question 7 of 7:

What is the importance of thermodynamics?

Thermodynamics is essential if you want to understand energy. If your plans are to build an engine, study the behavior of molecules, or find a more efficient way to prevent forest fires, you need a solid understanding of thermodynamics. Knowledge of thermodynamics is also a prerequisite for jobs in engineering, fossil fuel industries, aviation, and biology.^{[14]
X
Research source}
- Even if you don’t plan on working in a field related to thermodynamics, you can see the principles everywhere. Thermodynamics are why your appliances work when you plug them into the wall, and why 70 °F (21 °C) water feels cold on your skin, but air of the same temperature is comfortable!