Enthalpy Change in Thermodynamics

Enthalpy, abbreviated as H, can be defined as the total amount of energy or heat contained in a system or system component (including its components). Enthalpy is one of the most important and crucial variables to examine in the study of thermodynamics (the study of the interrelation between heat and other forms of energy). In order to comprehend the entire mechanics of a chemical reaction, it is required to measure the change in enthalpy that occurs over the course of the reaction. In order for a chemical (or biological) reaction to take place, there must be an exchange of energy in some form between the material undergoing the reaction and the environment in which it takes place. 

Enthalpy

When a system performing a chemical reaction requires an increase in energy intake, the enthalpy of the entire system increases; conversely, when the system releases a portion of its energy into the surrounding environment, the enthalpy of the entire system decreases. During a reaction, the portion of the energy contained within the molecules that can be used is referred to as the internal enthalpy or the enthalpy possessed by the system, while that portion of the energy contained within the molecules that is not related to the components or substances undergoing reaction is referred to as the external enthalpy or the enthalpy of the surroundings is referred to as the enthalpy of the surroundings.

The enthalpy H can be expressed mathematically as follows:

H = U +pV.

In this equation, H denotes the enthalpy of the system.

The internal energy of the system is denoted by the letter U.

The pressure in the system is denoted by the letter p.

The volume of the system is represented by the letter V.

Although the change in enthalpy (H) is measured instead of the quantity of heat that is directly observed, the amount of heat that is added or lost by the system is quantified as well. It is fully dependent on the state functions T, p, and U in order to perform properly.”

ΔH=ΔU+PΔV

Enthalpy Units are units of heat energy that are used in thermodynamics.

The following is a representation of the Enthalpy:

H = Energy/Mass

Dimensions can be used to represent practically any physical amount, and they are extremely versatile. A dimension’s units are the arbitrary magnitudes allocated to it, which are then used to determine the dimensions. Dimensions can be classified into two categories: basic or fundamental dimensions and secondary or derived dimensions. Basic dimensions are those that are inherent in the world around us.

Among the major dimensions are mass (m), length (L), time (t), and temperature (C) (T).

Among other things, secondary dimensions include those that may be calculated from primary dimensions such as velocity (m/s2) and pressure (Pa = kg/m.s2).

Units are currently available in two major systems: the SI (International System) and the USCS (United States Customary System), sometimes known as the English system. The SI (International System) is the most widely used system in the world. However, this course will strictly adhere to the use of metric units (often known as SI units). Because of the decimal link between units, the International System of Units (SI) units are based on this relationship.

The change in enthalpy

It is possible to estimate the change in enthalpy that will occur as a result of a chemical reaction by calculating the bond energy of the chemical process. The following activities must be completed in order to achieve this goal:

1. Prior to starting the reaction, we need to figure out which specific bond in the reactant molecules is most likely to disintegrate or break throughout the reaction. This is performed by the use of a kinetic study of the chemical reaction. After the bonds have been discovered, it is important to determine the bond enthalpy associated with those bonds; this information is readily available in the database.
2. As soon as we’ve calculated all of the bond enthalpy values for all of the bonds that are on the verge of breaking, we need to arithmetically sum up all of the numerical values we’ve gotten thus far.
3. We must also decide which bonds are expected to form at the end of the ongoing reaction, which theoretical numerical values are available in the database, and then combine them arithmetically to generate the new product at the conclusion of this reaction.
4. Never lose sight of the fact that the binding energies of each side should be assigned to the appropriate signals. In order to break bonds, the reactants require energy to enter the system; as a result, energy is supplied to them, and as a result, the bond energy values are always positive. Products, on the other hand, require the production of bonds, which releases energy from the system, and as a result, the sign of the bond energy values is always in the negative direction.
5. At this stage,one should combine the binding energies from both sides. For the bond energy value, multiply the total reactant bond energy value (added from the reactant side) by the total product bond energy value to obtain the bond energy value (added from the product side). When the final value is calculated, it represents the total enthalpy change that occurred throughout the reaction.

Conclusion

During chemical reactions, the enthalpy change occurs as a result of the bond breaking and making processes that take place in order to result in the production of some new products from the pre-existing reactants that were used at the start of the reaction. The bond breaking process always necessitates the use of energy (in the form of activation energy) in order to excite the electrons of the molecule to their excited state, where they collide with the molecules of the other reactant in order to commence the reaction and move it forward. As a result of this, any reaction that produces new final products is always more stable than either the initial reactants of the reaction or the intermediates formed during the course of the reaction. As a result, whenever a reaction produces new final products, it always releases energy into the surrounding environment. It can be expressed mathematically as the difference in potential energies of all of the total bond energies possessed by the products and reactants when a reaction is taking place. The change in enthalpy is represented by the symbol H.