Thermodynamics: Meaning, Laws, Applications

Introduction  

In physics, thermodynamic’s meaning covers more than just the transfer of energy. It relates to chemical reactions and matter as well. Thermodynamics physics is based on certain laws. These principles set the base for understanding fundamental properties in nature. To understand what thermodynamics is, first, we will need to define certain terms and concepts before we arrive at the laws. To simplify this vast field in physics, thermodynamics deals with heat, its transfer from one place to another, and understanding the effect it has on matter. Here we’ll go over the meaning, explanation, some important terms, and the laws of thermodynamics. 

What does thermodynamics mean?

In physics, scientists seek to understand, explain and predict natural phenomena. This includes things on microscopic scales (atoms and molecules) as well as on macroscopic scales (planets and galaxies). To be able to understand these things, we need to know certain measurable things, like size (volume), mass, temperature, and more. For example, you cannot understand the orbits of planets in our solar system unless you have some idea of the mass of the sun or the planets.

Just as understanding the velocity of objects is essential for much of physics, understanding the movement of heat or energy is also vital. Thermodynamics in physics seeks to use basic principles to understand the universe and various systems from the energy point of view. This is also heavily used in chemistry since thermodynamic concepts govern chemical reactions too. 

Here are just a few examples:

• If you mix hot water with cold water, the final mixture will be neither hot nor cold but warm
• A combustion engine takes in heat energy from the combustion reaction, which causes the gas’s temperature and pressure to increase forcing the piston to move, which shows how some of the heat energy is transferred to work done on the system
• The sun’s immense gravity causes the matter in it (mostly hydrogen) to undergo nuclear fusion and heat up, this heat is radiated outwards in all directions, and we receive that heat and light on the earth

Understanding all of these involve these processes, as varied as they are, require the use of thermodynamics’ physics. Before we jumpy into the laws of thermodynamics, let’s quickly define some fundamental concepts:

Basic Terms In Thermodynamics 

Temperature

Temperature is a measurement of the thermal energy of a substance or a system. It is based on various measurement scales like Celsius or Kelvin. 

Heat

Heat is the thermal energy that moves from one substance to another. Keep in mind that heat may also be converted into other things like work (kinetic energy) or light (electromagnetic radiation). 

Entropy

Entropy is a very important concept in thermodynamics, physics, chemistry, and cosmology. Entropy is a measurement of one aspect of a system. The quality we measure is the amount of wasted energy or energy that is not available to perform any work. An example of entropy is an ice cube melting. Initially, the ice is solid, with the water molecules being locked into a crystal and being rigid. This system has low entropy. When it melts into a liquid, the molecules flow freely and in a disordered manner. The entropy of this system is increased. Finally, if it is heated, then the ice turns to gas which is even more disordered, which is an even higher state of entropy. Entropy is also considered a measurement of randomness. 

The Laws of Thermodynamics 

There are 4 basic laws in thermodynamics. The last to be discovered was called law ‘zero’. It was found to be so fundamental that it needed to be stated before the other three (although laws 1, 2, and 3 had already been around much before the final law). 

The Zeroth Law of Thermodynamics

This law states that if bodies A and B are in thermal equilibrium with body C, then both A and B are also in thermal equilibrium with each other. Thermal equilibrium is the bedrock of our scientific explanation of temperature since we measure temperature in relation to other things. 

For example, we can take glass A filled with hot water and glass B filled with icy cold water. When placed into a room for some time, glass A and glass B will cool down or warm up to the temperature of the room. In this scenario, room C is our third body/system. After some time, we have two glasses, both of which are in thermal equilibrium with the room (they are both at room temperature).

If we were to pour the water from one glass to another, no thermal exchange would occur since they are at the same temperature, i.e., they are at thermal equilibrium.

The First Law of Thermodynamics

The First Law of Thermodynamics in physics states that the total amount of energy in an isolated system is always conserved. It cannot be created nor destroyed. That’s a bit hard to grasp, so let’s break it down. An isolated system is one in which nothing from the surroundings (neither matter nor energy) can enter the system. In reality, making a box that is 100% isolated from its surroundings is impossible, but the universe as a whole is a perfectly isolated system. 

Inside this isolated system, this law states that whatever energy is present inside it will remain present. It can be converted into other forms of energy such as work or heat, but the amount does not decrease.

Imagine a theoretical box that is completely isolated from everything else. Inside the box, we have a candle and air and a few bits of paper. If the candle is lit, the chemical reaction causes a release of heat, which in turn heats and moves the air. Moving air may do work on the pieces of paper and cause them to swirl around. When the candle is put off, the heat energy inside the system is conserved. It isn’t destroyed. 

The Second Law of Thermodynamics

This law states that the entropy of the universe or of all isolated systems will always increase and not decrease. This means that in any given system, chaos or disorder will always increase and not decrease. This assumes that there is no influence from external energy being put into the system.

We have already explained entropy in the earlier sections. This law simply states that everything in the universe is always moving towards higher entropy. Entropy allows for complexity (such as DNA, living beings, etc.) as long as the total entropy of the system is still increasing. 

The Third  Law of Thermodynamics

This law states that as the temperature of a perfect crystal reaches absolute zero, the entropy value for that system is also zero. Since this crystal is perfectly in order, it has no chaos meaning it cannot be at a lower state of entropy. And since it is at absolute zero, its molecules or atoms do not vibrate or produce any heat. 

Conclusion

Thermodynamics is a vast branch of science and can be used in chemistry and other sciences, but it is also used in our day to day lives. Engines, air conditioners, and electricity production need engineering thermodynamics principles to function.