Heat is a form of energy; and like any other form of energy it follows the laws of entropy. This means that heat or thermal energy goes from order to disorder. This change could also be rephrased as going from high concentration to lower concentration. This means heat wants to go from a hot place that has a lot of heat to a cold place with little heat; this is the 2nd law of thermodynamics.
Thermodynamics is the change (-dynamic) of heat (thermo-) and there are 4 basic laws that scientists use to describe this transformation of heat. The first law is similar to the conservation of energy and states “The change in the internal energy of a closed system is equal to the amount of heat supplied to the system, minus the amount of work performed by the system on its surroundings”. This basically says that the change of heat in a system equals the flow of heat and the energy required to complete a certain task within that system. In its entirety this first law just clarifies that the flow of heat is in fixed proportions and it does not magically appear or disappear.
The second law of thermodynamics as stated earlier simply states that heat always flows from hot to cold. This concept appears in many situations of science and this is because of entropy’s effect on energy.
The third law of thermodynamics states “At zero temperature the system must be in a state with the minimum possible energy”. Basically this is about how matter slows down as it gets colder. This is because there is less energy in the system and the matter has less energy it can use to move so it moves less. We also know it is technically impossible to reach absolute-zero (-273.15C, -459.67F, 0K) at the current time because we cannot stop all motion within a set of atoms. This is because matter moves, vibrates, stretches, and twists on all of its axis (x,y,z) and it is practically impossible to stop every single form of this motion to reach absolute zero.
The zeroth law of thermodynamics states “If two systems are in thermal equilibrium with a third system, they are also in thermal equilibrium with each other”. This is more of a math statement than a scientific one because it is simply the reflexive property… if A=C and B=C then A=B; this is an important mathematical idea to keep in mind but it is not really the essence of the chemistry taking place.
Now that we know the fundamental laws that apply to heat and how it moves we can apply them to every situation and figure out more precisely what is happening. In each situation we can define what our system is in our experiment and see what happens within our system and what happens between our system and its surroundings. This “system” is a basic model that is applied to many classical, statistical, and chemical situations that we break down and determine the essence of what is happening and how the heat itself is traveling by these 4 fundamental laws of thermodynamics.