The Laws of Thermodynamics

Thermodynamics is the science of how energy is transferred and used inside living systems. It uses the same laws of physics that describe how energy is exchanged between hot and cold objects, gas molecules, or anything else in our universe.

The first law of thermodynamics states that whenever heat is added to a system from outside, some of that energy stays inside the system and the rest gets converted into work. This 'law of conservation of energy' is important for our understanding of how all the exchanges of energy that take place in our bodies are possible, even though none of them are completely efficient.

It also explains why it is impossible for a living cell to use 100% of the energy that it receives. The energy that is not used to do work in the system is lost in a form that is unusable, which is often called waste energy.

Another important law of thermodynamics is that the entropy of a system increases when it gains heat or does work on its surroundings, and decreases when it loses heat or does no work on its surroundings. This increases the randomness in our world, making it harder for us to live efficiently and sustainably.

This law also tells us that a system's entropy will increase when it is isolated from its surroundings and if the surrounding conditions are not in harmony with the system. This includes conditions such as pressure, chemical potential, and temperature inhomogeneities.

Similarly, the second law of thermodynamics tells us that the entropy of a process will increase when it is nonspontaneous. This means that it is a process that is driven rather than natural. This can be seen in many processes like a chemical reaction.

The third law of thermodynamics tells us that a system in its ideal, stable state, has an entropy that is equal to zero at 0 K. This entropy is the sum of kinetic energy and potential energy, which are the energy that comes from motion of molecules or chemical bonds between molecules.

If this entropy increases, it will eventually reach zero, at which point the system is in thermal equilibrium. This can be seen by comparing the temperature of a liquid to the temperature of a solid or a gas to the temperature of its ambient air.

The first and second laws of thermodynamics are very useful for describing energy exchanges that occur within and between living systems. They are also important for describing the behavior of materials in our environment, such as how a hot metal can cool down and how a liquid can expand without being heated.