Chemical thermodynamics facts for kids

Kids Encyclopedia Facts

Chemical thermodynamics is a fascinating part of chemistry and physics that studies how heat and work are connected to chemical reactions and changes in the physical state of matter. It helps us understand why some chemical changes happen on their own (we call this spontaneity) and how much energy is involved.

This field uses the basic rules of thermodynamics to figure out how energy moves and changes during chemical processes. Scientists use both experiments in the lab and mathematical tools to explore these questions.

History
Overview
Chemical energy
Chemical reactions
- Gibbs energy
- Chemical affinity
Non-equilibrium
- System constraints
See also

History

J. Willard Gibbs is known as the founder of chemical thermodynamics.

The idea of chemical thermodynamics started to take shape in the late 1800s. In 1865, a German physicist named Rudolf Clausius suggested that the rules of thermochemistry (like how much heat is released when something burns) could be linked to the principles of thermodynamics.

Building on this, an American scientist named Willard Gibbs published important papers between 1873 and 1876. His most famous work was called On the Equilibrium of Heterogeneous Substances. In these papers, Gibbs showed how the first two laws of thermodynamics could be used with math and graphs to predict if chemical reactions would happen and when they would reach a balanced state (thermodynamic equilibrium). Gibbs's work brought together many ideas from other scientists like Clausius.

In the early 1900s, two key books helped make Gibbs's ideas widely used in chemistry. One was Thermodynamics and the Free Energy of Chemical Substances (1923) by Gilbert N. Lewis and Merle Randall. This book helped popularize the term "free energy". The other was Modern Thermodynamics by the methods of Willard Gibbs (1933) by E. A. Guggenheim. Because of their big contributions, Lewis, Randall, and Guggenheim are seen as the founders of modern chemical thermodynamics.

Overview

The main goal of chemical thermodynamics is to figure out if a certain change or reaction is possible and if it will happen on its own. It helps us predict the energy changes in processes like:

Chemical reactions (when chemicals change into new ones)
Phase changes (like ice melting into water or water boiling into steam)
The creation of solutions (like sugar dissolving in water)

To do this, chemical thermodynamics focuses on several important properties of a system. These are called state functions because their value only depends on the current state of the system, not how it got there. The main ones are:

Most of the rules in chemical thermodynamics come from applying the first and second laws of thermodynamics to these state functions. The most important rule is the law of conservation of energy.

Here are the three main laws of thermodynamics in simple terms: 1. The total energy in the universe always stays the same. It can change forms, but it's never created or destroyed. 2. In any process that happens naturally, the total entropy (a measure of disorder or randomness) of the universe always increases. Things tend to get more spread out and disordered over time. 3. The entropy of a perfectly ordered crystal at absolute zero temperature (0 Kelvin) is zero. This means at the coldest possible temperature, a perfect crystal has no disorder.

Chemical energy

Chemical energy is the energy stored within the bonds of chemical substances. This energy can be released or absorbed when these substances undergo a chemical reaction and their bonds break or new ones form. Often, this energy change shows up as heat.

When a chemical reaction happens, the energy released (or absorbed) is the difference between the energy stored in the starting chemicals (reactants) and the energy stored in the new chemicals formed (products). This change is called the change in internal energy. If a reaction happens in a closed container where the volume doesn't change, the heat measured is equal to the internal energy change. However, if the reaction happens in an open container (like a beaker in a lab), the pressure stays constant, and some energy might be used for work (like pushing air), so the heat measured is called the enthalpy change.

A common example is the heat of combustion, which is the chemical energy released when something burns. This is important for understanding fuels. Even the food we eat is like a fuel; when our bodies process it, chemical energy is released, similar to how a car uses gasoline.

In chemical thermodynamics, the idea of "chemical potential energy" is often called chemical potential. It helps us understand how chemicals want to move or react.

Chemical reactions

In chemical thermodynamics, we often look at how the amounts of different chemicals change during processes like chemical reactions or phase transitions (like melting or boiling). These changes usually create more entropy (disorder) in the universe unless they are perfectly balanced or carefully controlled.

Gibbs energy

The Gibbs free energy (often just called Gibbs energy, symbolized as G) is a very important concept. It helps us predict if a chemical reaction will happen on its own at a constant temperature and pressure, which are common conditions in labs and in living things.

Think of it this way: if the Gibbs energy of a system goes down during a process, that process tends to happen naturally. It's like a ball rolling downhill – it naturally goes to a lower energy state.

When a chemical reaction happens, the Gibbs energy changes. Scientists use a special way to describe this change, especially when looking at how much a reaction has progressed.

Chemical affinity

The idea of "chemical affinity" helps us understand how much different chemicals "like" to react with each other. If chemicals have a strong affinity, they are very likely to react.

Imagine you have a reaction where chemicals A and B turn into C and D. The "extent of reaction" tells us how far along this reaction has gone. The change in Gibbs energy related to this progress is linked to the chemical affinity. If the Gibbs energy decreases (meaning the reaction wants to happen), the chemical affinity between the reactants is positive.

This means that if a reaction is happening on its own, it's because the chemicals involved have a positive affinity for each other, and the Gibbs energy of the system is decreasing. This decrease in Gibbs energy can be used to do useful work, or it can simply be released as heat, increasing the disorder (entropy) of the surroundings.

Non-equilibrium

Most of the time, traditional chemical thermodynamics looks at systems that are either perfectly balanced (thermodynamic equilibrium) or very close to it. However, many real-world systems, especially living ones, are far from equilibrium.

A scientist named Ilya Prigogine developed a new way to understand the thermodynamics of open systems that are far from equilibrium. He discovered that in these systems, amazing things can happen. Even though the second law of thermodynamics says things tend to become more disordered, Prigogine showed how ordered structures can actually develop from disorder in these open systems.

He called these "dissipative systems" because they need a constant exchange of energy with their environment to stay organized. If this energy exchange stops, they fall apart. Think of a living cell: it constantly takes in nutrients and releases waste, using energy to maintain its complex structure. If it stops, it dies.

Prigogine's ideas have been used to explain many different complex systems, from how cities grow to how biological structures develop. It shows that even in a universe that tends towards disorder, local pockets of order can emerge and be maintained through energy flow.

System constraints

It's important to remember that chemical reactions and processes don't always happen freely. They can be affected by "constraints" like walls, pistons, or electrical wires.

For example, if a gas reaction produces more gas molecules, it will try to expand. If it's in a cylinder with a piston, it can only expand by pushing the piston out, doing work. If you push the piston in, you can force the reaction to go backward.

Another example is a redox reaction in a battery. The chemical reaction creates an electric current that can power a device or do mechanical work (like running a motor). You can also recharge the battery, forcing the chemical reaction to go backward by applying electricity. In these cases, the chemical reaction isn't an independent process; it's linked to something else doing work.

Even in living things, processes are coupled. For instance, the breakdown of ATP (a molecule that carries energy in cells) provides the energy for muscles to move. And the creation of ATP is powered by other chemical reactions in tiny parts of cells called mitochondria. This shows how different chemical processes are connected and depend on each other to make things happen.