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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.

What Is 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.

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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.

Systems in Chemical Thermodynamics

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 flask, we can either call the coffee itself the system, or the whole thermos flask (including the walls of the container).There are several types of systems in chemical thermodynamics: isolated systems, closed systems, and open systems.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
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 (the room) to cold places (the refrigerator) just like normal.

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

Four State Functions

The four numbers that define the state of a system are internal energy, enthalpy, entropy and Gibbs free energy.

We’ve already talked about the entropy (disorder) of a system, so let’s define the other three.The internal energy of a system is the total kinetic and potential energy of all the particles in the whole system. Or in other words, it’s the combination of the movement energy of the particles and the potential those particles have for movement. This is kind of like how a ball at the top of a hill has the potential to roll down that hill.

It is measured in joules.The enthalpy of a system is the heat gained or lost by a system during a chemical reaction at a constant amount of pressure. It’s equal to the internal energy lost by a system plus the work done by the system on the surroundings. It is measured in joules per kilogram.

The Gibbs free energy is the maximum amount of work that can be extracted from a closed system, not counting volume expansions. It’s the amount of useful energy that can come out of the system in ways that don’t involve pushing a piston or otherwise expanding the space the gas is in. It is measured in joules per mole.Chemical thermodynamics often involves using complex and equations and statistics to figure out these four numbers.

Lesson Summary

Chemical thermodynamics is the study of how heat and work relate to each other both in changes of state and in chemical reactions. Key principles of chemical thermodynamics include systems, the laws of thermodynamics, and the four state functions.

Systems are the particular object or set of particles you’re looking at. Isolated systems don’t allow energy or mass to move in or out. Closed systems don’t allow mass to move in or out.

And open systems allow both to move in or out.The first law of thermodynamics says that the change in energy inside a system is equal to the heat energy added to the system, minus the work done by the system. The second law of thermodynamics says that the entropy of the universe always increases, which also means that heat can only go from hot places to cold places unless you do work (add energy).The four state functions, or numbers that define a system, are internal energy, enthalpy, Gibbs free energy, and entropy. Internal energy is the total kinetic and potential energy of the system.

Enthalpy is the heat gained or lost by a system during a constant-pressure chemical reaction. Gibbs free energy is the maximum work that can be taken from a closed system, without changing the volume. And entropy is the disorder of the system.

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