The operation of a refrigerator can be understood in terms of two statements that reflect the second law of thermodynamics:
Heat flows spontaneously from a colder object to a hotter object: The first statement relates to the natural direction of heat transfer. In the case of a refrigerator, this principle implies that heat is extracted from the colder interior of the refrigerator and expelled to the hotter external environment. It is in contrast to the intuitive expectation that heat should flow from hot to cold. By using energy in the form of electricity, the refrigerator actively pumps heat against its natural tendency to flow from cold to hot.
Entropy increases in a closed system: The second statement refers to the concept of entropy, which is a measure of the disorder or randomness in a system. According to the second law, the total entropy of an isolated system, such as the combination of the refrigerator and its surroundings, tends to increase over time. In the case of a refrigerator, it means that the removal of heat from the interior of the refrigerator causes a decrease in entropy inside, but this is compensated by an increase in entropy in the external environment as heat is expelled. The overall entropy of the system increases, satisfying the second law.
In summary, a refrigerator functions by actively transferring heat from a colder region to a hotter region, in opposition to the natural flow of heat. It maintains the overall increase in entropy by compensating for the reduction of entropy inside the refrigerator with an increase in entropy in the external environment.