Final answer:
Enthalpy (H) is the total energy of a system and is defined as the sum of its internal energy (U) and the product of its pressure (P) and volume (V). Internal energy (U) represents the average mechanical energy of the system's components. Entropy (S) is a measure of disorder within a system and is related to the change in internal energy, temperature, and work.
Step-by-step explanation:
Enthalpy (H) is defined as the sum of a system's internal energy (U) and the product of its pressure (P) and volume (V). It represents the total energy of a system.
Enthalpy can be used to describe the energy changes that occur in chemical reactions.
For example, the enthalpy of formation (AH₁) is the energy change involved in the formation of 1 mole of a compound from its component elements.
Internal energy (U) is the sum of the kinetic energy and potential energy of all the molecules or entities in the system. It represents the average of the total mechanical energy of the system.
Changes in internal energy produce heat and work.
Entropy (S) is a measure of randomness or disorder within a system.
It is related to the change in internal energy, the absolute temperature, and the work done by the system.