Chemistry

Difference Between Enthalpy and Internal Energy

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Main Difference

The main difference between Enthalpy and Internal Energy is that Enthalpy is the process of heat-absorbing or released during a chemical reaction that usually occurs in an arrangement, whereas Internal Energy is normally the sum of potential energy and kinetic energy in an arrangement.

Enthalpy vs. Internal Energy

Enthalpy is considered as the heat energy, which is generally being absorbed or evolved during the advancement of a chemical reaction. Internal energy considered as the system energy, which is usually the sum of potential energy and the kinetic energy that is present in the system or an arrangement. The equation of enthalpy from which it is measured is generally given as H = U + PV, whereas the equation of internal energy, which is generally used to measure internal energy, is given as delta U = q + w.

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Enthalpy is defined in another way that it is the general relationship between the system and the surrounding; on the other hand, the internal energy is considered as the total energy present in a system. When the heat released or absorbed during a reaction in enthalpy, which goes at persistent pressure, is generally equivalent to the conversion (delta) in the enthalpy. On the contrary, in internal energy, when the heat released or absorbed during a reaction, which goes at unceasing volume is usually equivalent to the alteration in the internal energy of the system.

The change which is present in the enthalpy of the system throughout a chemical reaction is generally equal to the change present in the internal energy, and additionally, a major difference is present in the product of the pressure of the gas present in the system and its volume (PV).

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In solids and liquids, the change which is considered in enthalpy of the system is small because there is present a little change in the volume of the system during the reaction. On the other hand, in liquids, the change is considered for the internal energy of the system because there is also, if any, present a little change in the volume of the system during the reaction.

Comparison Chart

EnthalpyInternal Energy
Enthalpy refers to heat energy, which is generally being absorbed or evolved during the process of a chemical reaction.Internal energy is generally referred to as the system energy, which is usually the sum of potential energy and the kinetic energy that is present in the system.
Equation
H = U + PVDelta U = q + w
System
It is the general relationship between the system and the surrounding.It is considered as the total energy present in a system.
Constant Pressure/Volume
The heat released or absorbed during a reaction that runs at constant pressure is generally equal to the change (delta) in the enthalpy of the system.The formed heat released or absorbed during a reaction that runs at constant volume is usually equal to the alteration in the internal energy of the system.
Equal Change
The change which is present in the enthalpy of the system throughout a chemical reaction is generally equal to the change present in the internal energy.Change of enthalpy is generally equal to the change present in internal energy.
Product of Pressure and Volume
Difference in PVDifference between PV
In Solids and Liquids
The change which is considered is present a little change in the volume of the system during the reaction.The change which is considered is also, if any, present a little change in the volume of the system during the reaction.
For Gases
Large change comes when an alteration in the number of moles of gas occurs in the reaction.Large change comes when an alteration in the number of moles of gas occurs in the reaction.

What is Enthalpy?

The term enthalpy generally refers to heat energy, which is normally being absorbed or evolved during the process of a chemical reaction. Enthalpy of the system is symbolized by H, in which H usually indicates the total amount of energy. The change which is present in enthalpy is given as delta H, where the delta generally refers to the change of enthalpy.

The units in which enthalpy is given are usually in joules (j) or kilojoules (KJ). In enthalpy, when the heat released or absorbed during a reaction which runs at constant pressure is generally equal to the change (delta) in the enthalpy of the system which is given asH = U + PV where H is considered as the enthalpy, U is used for the sum of the internal energy, P is normally the pressure of the system, V is considered as the volume of the system.

Hence, this equation proves that the enthalpy is the sum of the internal energy and normally the energy which is required for the maintenance of the volume at a given system and a given pressure. The term “PV” in equation specifies the work that has to be completed on the environment present outside the reaction to make space for the system.

The change of enthalpy (delta) generally refers to whether a particular reaction that is carried out is an exothermic or endothermic reaction. The reaction will be considered as exothermic when delta H has a negative value, and the energy releases outside. On the other hand, the reaction will be considered as endothermic when delta H has a positive value, which generally means that the energy should be given to the system from the outside.

What is Internal Energy?

The term internal energy usually refers to the system energy, which is usually the sum of potential energy and the kinetic energy that is present in the system. Potential energy is considered as the stored energy of the system, whereas kinetic energy is considered as the generated energy of the system produced by the motion of molecules. The internal energy of the system is generally symbolized by U, and the change in internal energy is written as delta U.

In internal energy, when the heat released or absorbed during a reaction which runs at constant volume is usually equal to the alteration in the internal energy of the system, and it is given as delta U = q + w where Delta U is generally the change in internal energy, q is considered as the heat transfer, w is the work done by and on the system.

Though the term delta U is not considered for the isolated system because internal energy is constant, the transfer energy is constant, and also the work done is zero. If its value is positive, then the system absorbs heat, and if it is negative, then the system releases heat. Internal energy can exist as potential or kinetic energy but not as heat or work.

Key Differences

  1. Enthalpy is the heat energy that is mostly being absorbed or evolved, while internal energy is deliberated as the system energy, which is normally the calculation of potential energy and the kinetic energy.
  2. The equation of enthalpy is given as H = U + PV, whereas the equation of internal energy is given as delta U = q + w.
  3. The association between the system and the surrounding is an alternative way to define Enthalpy; on the other hand, the total energy present in a system is considered as the internal energy.
  4. In enthalpy, the heat goes at constant pressure is equivalent to the variation (delta) in the enthalpy of the system; on the contrary, in internal energy, the heat goes at constant volume is equivalent to the change in the internal energy of the system.
  5. The difference which is existing in the enthalpy of the system during a chemical reaction is usually equivalent to the alteration existing in the internal energy in the system.

Conclusion

The above discussion concludes that the major difference among enthalpy and internal energy is present in the product of the pressure of the gas present in the system and its volume (PV) and shows that enthalpy is the process of heat-absorbing or released during a chemical reaction that usually occurs in an arrangement. Internal energy is normally the sum of potential energy and kinetic energy in an arrangement.

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Harlon Moss

Harlon currently works as a quality moderator and content writer for Difference Wiki. He graduated from the University of California in 2010 with a degree in Computer Science. Follow him on Twitter @HarlonMoss