Enthalpy (H) is a thermodynamic property that represents the total heat content of a system. It takes into account both the internal energy (U) and the work (pV) done by the system. Enthalpy is often used to describe the heat transfer that occurs during a chemical or physical process.


The correct definition of enthalpy is given by option 'A': H = U + pV.


Let's break down the equation to understand each term:

U: Internal Energy
Internal energy (U) is the sum of all the microscopic energies of a system. It includes the kinetic and potential energies of the particles within the system. The internal energy depends on the temperature and the state of the system.

pV: Work Done by the System
Work (pV) refers to the mechanical energy transferred by the system to its surroundings or vice versa. It represents the product of pressure (p) and volume (V) of the system. If the system expands, work is done by the system (negative sign), and if the system is compressed, work is done on the system (positive sign).

When enthalpy is defined as H = U + pV, it takes into account the internal energy of the system and the work done by the system. This equation allows us to calculate the total heat content of the system, including both the heat absorbed or released during a process and the work done by the system.


Enthalpy is a useful concept in thermodynamics as it provides a convenient way to express the heat transfer in a process. In chemical reactions, the change in enthalpy (ΔH) can be used to determine whether a reaction is exothermic (ΔH < 0)="" or="" endothermic="" (δh="" /> 0). Enthalpy is also used to calculate heat capacities, enthalpies of formation, and to analyze energy changes in various processes.

In conclusion, enthalpy is a thermodynamic property that combines the internal energy and work done by a system. The correct definition of enthalpy is given by option 'A': H = U + pV. This equation allows us to calculate the total heat content of a system and is useful in analyzing chemical reactions and energy changes.