Enthalpy is a combination of two Greek words, entheilai (heil) which means “heavenly heat” and phonograph (iasm) which means “motion”. According to Martin schemer, the relationship between energy and temperature as studied by thermodynamics is the concept of thermodynamic constant pressure. Thermodynamics enthalpy refers to the study of heat or the energy exchanged in a system with surroundings at rest. In this state of system, there is no change in the total amount of heat in the system.
The study of thermal energy involves the study of internal energy and external energy. It also involves time and the lapse of time. Thermodynamics enthalpy is related to the classical mechanics of fluid mechanics. The difference between the theory and practice is the focus on the concept of potential energy. In a thermodynamic system, no external source of energy can be identified that can create a change in the total internal energy of the system.
This definition of enthalpy is based on the assumption that the total internal energy is conserved in all states of the system. In most cases, it is not. In the state of steady state, no changes are made that could affect the state of thermal energy. In thermodynamic systems, heat produced in one state is changed into energy required for the next step, the heat flowing from a colder state into the hotter one is changed into energy that needs to be transferred from one state to another and so on.
When a system has a state of thermal enthalpy, it means that the internal energy is the same throughout the system. In such systems, it is a qualitative equilibrium state. Any change in state, whether it is thermal or potential energy, can only affect the probability of the state of equilibrium being changed back to its original state.
Thermodynamics enthalpy relations determine the relationship between enthalpy and thermal energy. These relationships show how energy can be transformed from a higher state of thermodynamic energy to a lower one, depending on the state of equilibrium. For instance, the overall average temperature is found to be a perfect state of thermodynamic energy. The temperature continues to increase because there is no heat flowing from a warmer state into a cooler one.
There is also enthalpy that exists when heat is flowing from a hot body to a cooler body at the same time. This enthalpy is called the evaporation heat. When heat is flowing from a hot body to a cooler body at the same time, the overall average temperature will decrease. Enthalpy diagrams depict the relationship between enthalpy and temperature change. These relationships show that the total amount of energy change, in any state of thermodynamic equilibrium, can be linearly correlated with the changes in the enthalpy value of that state.
Thermodynamics enthalpy diagrams are typically presented in two forms. One form depicts a steady state curve with successive highs and lows representing the changes in enthalpy. The other form depicts a dynamic state curve with the ups and downs of enthalpy changing as a function of changes in state of heat flux. This form is easier to understand since the curves appear as a power law or a U-shape. The U-shape resembles a football where each point represents an energy gradient, or change in the enthalpy of a system. This allows for easier visual interpretation of the enthalpy changes.
There are a number of thermodynamic relationships that are important in understanding thermodynamics. They include the Claus-Kreiser-Rankine relationship, the exponential heat evolution, the thermodynamic trade-off, and the gauge equations. Understanding each of these relationships and their variations in a way that illustrates enthalpy is crucial in the study of thermodynamics. Enthalpy diagrams are often introduced into courses that teach students the concepts of heat transfer, and climate.