Chemical Thermodynamics: Definition & Principles Video

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  • 0:04 Chemical Thermodynamics
  • 1:00 Systems
  • 1:46 Laws of Thermodynamics
  • 3:09 Four State Functions
  • 4:21 Lesson Summary
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Lesson Transcript
Instructor: David Wood

David has taught Honors Physics, AP Physics, IB Physics and general science courses. He has a Masters in Education, and a Bachelors in Physics.

Learn about chemical thermodynamics and explore some of its basic principles, including systems and the laws of thermodynamics. See how well you grasp the principles at the end of the lesson by taking a quick quiz.

Chemical Thermodynamics

Do you have a refrigerator in your home or an engine in your car? Both of those things work on the principles of thermodynamics.

Have you ever noticed how it's hotter upstairs in your home than downstairs? That's also thermodynamics. And the way a thermos flask can keep your coffee warm? Yup, you guessed it: thermodynamics.

Chemical thermodynamics is the study of how heat and work relate to each other both in changes of state and in chemical reactions. It involves a series of rules and laws that explain how heat and work, well, work, and explains which processes can happen spontaneously and which need some help.

There are several basic principles of chemical thermodynamics to consider: systems, the laws of thermodynamics, and enthalpy. Chemical thermodynamics is also concerned with four particular quantities: internal energy, enthalpy, entropy, and the Gibbs free energy. Let's look into all these in more detail.


To understand thermodynamics, it's helpful to first define something called a system. A system is a series of components that are connected together. In a nutshell, it's the part of the world we're focusing on. We can look at what moves in and out of a particular system. For example, if we have coffee in a thermos, we can either call the coffee itself the system, or the whole thermos (including the walls of the container).

There are several types of systems in chemical thermodynamics. An isolated system is one that has rigid walls and doesn't allow the transfer of energy or mass. The walls are perfectly insulating. A closed system has walls that let energy pass in and out of the system, but that don't allow mass to enter or escape. And an open system allows both energy and matter to enter and leave.

The Boundary of a System Defines It
The Boundary of a System Defines It

Laws of Thermodynamics

There are several important laws of thermodynamics that form the cornerstone of the field. The first law of thermodynamics says that the change in the internal energy of a closed system equals the heat added to the system, minus the work done by the system on the surroundings. This also means that in an isolated system, the energy changes inside the system must be zero.

The second law of thermodynamics says that the entropy in the universe must always increase. Entropy is the amount of disorder in the universe, measured in joules per kelvin. So this means the universe always becomes more disorderly. Let's say that you decide to tidy up your home: you put away the books in alphabetical order, wash the dishes, and store them in neat piles. You might think you've just made the universe more orderly, and in some ways you have, but in the universe as a whole this is impossible. By using your muscles to tidy things up, you've produced heat energy in your arms, and that heat energy has overall made the universe less orderly.

Gases are more disorderly than liquids and solids, and so have a greater entropy
Gases are more disorderly than liquids and solids, and so have a greater entropy

Another consequence of the second law of thermodynamics is that heat can only travel spontaneously from hot places to cold places. This means that a refrigerator can't work on its own. The only way to make a refrigerator work is by doing work - by using energy from the electricity supply in the wall. Turn off the electricity, and heat will move from hot places (like the room) to cold places (like the refrigerator) just like normal.

Heat Travels from Hot Places to Cold Places
Heat Travels from Hot Places to Cold Places

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