The enthalpy is useful to heat content in a system, but the answer of “is enthalpy a state function” is given as,
Yes, because Some of the other state functions give it. There is no any dependency of followed path for state functions.
The enthalpy of the substance is measured to check heat transfer between the confined space and the surrounding with constant paper. It is thermodynamic quantity.
In thermodynamics, there are two types of functions (1) State function (2) Path Function.
The property of state function depends on the particular state. Generally, the state functions are expressed as a difference between the process starting state and process completion state. The intermediate state consideration in the calculation of state function is avoided.
There is no relation of state function with the followed path of the process. The value of the state function does not related with the process path.
The enthalpy is the property that can be well understood by the following expression,
h = u + PV
The above equation is famous for defining the enthalpy in thermodynamics.
- h = Enthalpy of the substance or system (Joule)
- u = Internal energy of the system (Joule)
- p = Pressure (N/m2)
- v = Volume (m3)
The first law of thermodynamics provides information on calculating the system’s enthalpy.
The multiplication of the pressure (p) and volume (v) is the form of energy. With the definition of the state function, We can say that the pressure, volume and internal energy are the state functions. If these three are state functions, we got the answer, “Is enthalpy a state function”.
The value of the path functions is monitored throughout the path of the process. At every place or stage on the path, The value of the path function is related. Do you know the two most popular path functions in thermodynamics?
Work and heat
The enthalpy calculation is formulated by the use of initial temperature of the process and the final temperature of the process. There is no entertainment of any intermediate value during this calculation.
Examples of state function
The state functions are also known as state variables in thermodynamics.
- Enthalpy (h)
- Entropy (S)
- Internal energy (u)
- Pressure (P)
- Volume (v)
- Temperature (T)
- Free energy
- Density (ρ)
The above is the list of properties that depends on the state. The value is noted for initial stage and the final stage.
In the case of enthalpy, The internal energy, pressure and volume are fall in the above list. Enthalpy is expressed as the sum of I.E and the pressure – volume product. The sum of the all-state functions states that the enthalpy falls in the list of state functions.
Why are internal energy, pressure and volume state functions?
The two most common state functions are pressure and temperature
The change is that these properties are more important than the path followed to make a change.
Let’s understand it with one practical example,
Suppose we have two cups filled with tea. The temperature in both cups is different, 30 °C and 40 °C, respectively. The atmospheric temperature is considered 20 °C under normal conditions. The transfer of heat will take place from cups of tea to the atmosphere. The values of the properties are varying in the initial and the final stage.
Now, what will happen in internal energy, enthalpy and entropy?
The tea density will be different compared with the initial state. If we talk about enthalpy, pressure, internal energy and volume, Their values depend on the present state rather than on the past.
The enthalpy h has a linear relation with the internal energy (u), pressure (p) and volume (v) product. The values of the enthalpy directly depend on the above three properties.
There are two enthalpies in the chemistry, the Enthalpy of the formation and the enthalpy of the reaction.
What is a state function?
There are two terms like state and path function in the thermodynamic.
The state function is one whose value is calculated concerning the initial state and final state. The intermediate value is not monitored.
The path followed by the process does not matter for the state function. There are many properties in thermodynamics measured on a state like pressure, temperature, enthalpy etc.
Heat and work are two famous terms in thermodynamics to be path functions. The heat and work are not measured at a particular point, but it is measured as the heat transferred through the process or path followed. The work is done through the process or followed a path.
Let’s take an example to understand this concept,
Suppose I have a glass of water. The initial temperature of the water is 30 °C. We are supplying some heat to the glass, so the water temperature is raised and reaches 50 °C.
According to state function, The temperature change is more important. Rather than by which method or path we have increased water temperature.
I am Deepak Kumar Jani, Pursuing PhD in Mechanical- Renewable energy. I have five years of teaching and two-year research experience. My subject area of interest are thermal engineering, automobile engineering, Mechanical measurement, Engineering Drawing, Fluid mechanics etc. I have filed a patent on “Hybridization of green energy for power production”. I have published 17 research papers and two books.
I am glad to be part of Lambdageeks and would like to present some of my expertise in a simplistic way with the readers.
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