Heat Internal Energy and Enthalpy

In thermodynamics, we examine changes in the state caused by the combined action of heat and work. Specific rules govern the changes and their consequences, referred to as thermodynamic laws. Different chemical processes transform heat energy into various useful forms using thermodynamic principles. This is the essence of energy transformation: we cannot create or destroy energy, but can only change from one form to another. An example of thermodynamics is the process of converting energy from one form to another. It also studies the process of converting heat to temperature and labour and energy.

Thermodynamics studies the relationship between heat, internal energy, and work within a system. It was William Thomas who coined the term thermodynamics in 1749. The rules of thermodynamics relate to changes of energy that occur during a reaction, not to its rate of occurrence. Let’s review some of the most common thermodynamic terms, such as enthalpy,  heat and internal energy, and then ensure that we understand them completely.

Read on to know more about the  enthalpy, heat and internal energy 

Heat 

Thermodynamics examines several properties of matter, chief among them being heat. Heat transfers contribute to the change in a system’s internal energy or enthalpy, which are fundamental variables in thermodynamics. A thermodynamic definition of heat is “energy in motion.” Heat moves from a higher to a lower temperature. Heat is the energy travelling through temperature disparities. Temperature and heat are often used interchangeably, but this is inaccurate. Even if two bodies of the same material receive the same amount of heat, their temperatures will differ. The material’s heat capacity (C) is the cause of this temperature difference. Heat capacity refers to the ability of a material to store and release heat without modifying its temperature. Heat capacity correlates with conductivity pretty well since high heat capacity materials are generally good insulators and low heat capacity materials are good conductors. When heat enters the system, it is considered positive; when heat leaves, it is considered negative. Heat equation can be expressed as follows :

Q=mc△T

Where Q is heat transfer ( cal or J) , m is mass  ,c is specific heat(J/g/K) and△T is change in temperature

Heat flow is affected by the following factors:

1. Substance mass.
2. Differing temperatures between two objects.
3. Substance nature.                                                                                                                                                                                                   

   Internal Energy

                                                                                                                                                                           

One of the important properties of thermodynamics is the internal energy of any substance. Internal energy is seen as the combination of potential energy and kinetic energy present inside a system. In the measurement of internal energy, Joule is used. Temperature, starting state, and ending state all affect internal energy. Understanding the internal energy of a system can be accomplished by taking a look at the simplest system possible, an ideal gas. Ideal gases do not have potential energy because particles do not interact. An ideal gas’ internal energy is determined by the kinetic energies of its particles. A gas’s temperature is directly proportional to its particle kinetic energy under the molecular theory of kinetic energy. In complex systems, internal energy cannot be determined directly. The temperature remains a determinant of the system’s internal energy. Observing a system’s temperature allows us to determine how its internal energy is changing. We can infer that when the temperature of the system rises, it is also increasing its internal energy.

The internal energy possesses two very important following properties similar to other thermodynamic variables: 

1. It is a function of state
2. Extensive scales.

It is possible to change the internal energy through two mechanisms. One is through heat transfer through either absorbing or releasing it into the environment. Alternatively, one can change internal energy by doing work. Based on this, we can say that internal energy changes as follows:

∆U = q + w

∆U= changing of the internal energy

q= heat that is transferred 

w= using the system or working with it

Although internal energy exists in kinetic or potential form, there is no heat or work, since heat and work only occur when the system is altered.

Enthalpy

In a system, enthalpy represents the energy contained within. Chemical reactions involve the absorption and release of heat energy, referred to as enthalpy. The H symbol represents it. Enthalpy changes are represented by the symbol ∆H, where ∆ indicates a change in enthalpy. An enthalpy can either be expressed in joules or kilojoules. ∆H must be positive for the reaction to be endothermic. This means energy must be supplied from outside the system to trigger the reaction. In contrast, a negative value of ∆H indicates that energy is released into the surrounding environment. In addition, the enthalpy of substances can change as their phases or states change. For example, the heat of fusion occurs when a solid becomes a liquid. The heat of vaporization pertains to the enthalpy change that occurs when a liquid turns into a gas. In a system, temperature plays a large role in determining the enthalpy. The kinetic energy of molecules increases with higher temperatures, increasing the internal energy of a system. This results in increased enthalpy.

A constant pressure process has the following enthalpy:

H= U+PV

H= the enthalpy

U= internal energy sum

P= system pressure

V= system volume

PV indicates that work is needed to make space for the system in the environment. 

Adding an electron to the atom can be an endothermic or exothermic reaction. When an electron is added to the atom, there is a release of energy. As a result, electron gain enthalpy is negative.

Conclusion 

Two main parts of the universe are the system and the surroundings. Essentially, the system comprises the chemical and physical process of interest and everything else contained by the surrounding area. This definition allows one to solve numerous practical problems within thermodynamics or the transfer of energy. The system either releases or absorbs heat during the reaction. As well as this, the system either affects its surroundings or is affected by them. In both cases, the system’s internal energy can be affected.