The difference is [itex]P V[/itex].Taturana said:What's the difference between enthalpy and internal energy?
Taturana said:What's the difference between enthalpy and internal energy?
Internal energy is the average of the kinetic energy (linear and angular) of the particles of the body (or system), right?
Could someone explain me this clearly?
Thank you
Andy Resnick said:That's a good question. First, consider the total energy E of a body or system:
E = KE + PE + U
Where KE is kinetic energy, PE potential energy, and U the 'internal energy'. Internal energy is energy that cannot be accounted for by specifying position, velocity, or mass. It's not a mechanical form of energy, it's (essentially) heat energy. It's related to temperature as well.
Enthalpy H = U + PV.
If U is the heat energy, PV is the 'work' energy. Enthalpy is also the total amount of energy available in a system or body, like E, but written using thermodynamic variables instead of mechanical variables. Changes in enthalpy occur during a thermodynamic process involving the conversion of heat into work (or vice-versa).
internal energy is energy that cannot be accounted for by specifying position, velocity, or mass.
Studiot said:I think this is a very good quote, if you exclude the mass.
Andy, are you sure you want to include mass, isn't internal energy an extensive property, ie twice the mass means twice the internal energy, all other things being equal?
Enthalpy and internal energy are both thermodynamic properties that describe the energy of a system. However, enthalpy specifically refers to the amount of heat that is released or absorbed during a process, while internal energy refers to the total energy of the system, including the kinetic and potential energies of its particles.
Enthalpy is often more useful than internal energy because it takes into account the work done by or on the system during a process. This makes it a more practical and measurable quantity in many real-world situations, such as chemical reactions or power generation.
Yes, enthalpy and internal energy can be equal in certain cases, such as when there is no change in volume during a process. In this case, the work done by or on the system is zero, so the enthalpy will be equal to the internal energy.
Enthalpy and heat are closely related, as enthalpy is defined as the amount of heat released or absorbed during a process at constant pressure. This means that the change in enthalpy is equal to the heat transferred at constant pressure, and vice versa.
Enthalpy is typically measured using a calorimeter, which is a device that measures the heat absorbed or released during a process. This allows for the calculation of the change in enthalpy, which can then be used to determine the enthalpy of the system before and after the process.