Why we needed to define enthelpy?

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In summary, the introduction of the enthalpy term was necessary because it allows for a more accurate measurement of heat under constant pressure. This is because eliminating volumetric work in the equation dU = dq - p·dV is difficult in practice, but the definition of enthalpy as H = U + p·V allows for the elimination of non-volumetric work and results in a simpler equation, dH = dq + V·dp, which is easily measured under constant pressure.
  • #1
Frigus
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If we know that at constant pressure heat absorbed or gained is path independent then what was the need for introducing this new enthalpy term.
If its answer is that it is not only for a special case in which pressure is constant then how can we even use it because we cannot measure the internal energy.
Thanks
 
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  • #2
I don't understand your question. Please provide a specific problem (with actual temperatures, pressures, amounts of material, etc) that better illustrates what your issue is.
 
  • #3
Hemant said:
If we know that at constant pressure heat absorbed or gained is path independent then what was the need for introducing this new enthalpy term.

The change of internal energy is dU = dq + dw. It is easy to eliminate non-volumetric work. But than you still have dU = dq - p·dV. Eliminating the volumetric work would require keeping the volume constant which is difficult in practice. That means that an accurate calorimetric measurement would always need to be accompanied by a measurement of the change in volume.

This problem is solved by the definition of enthalpy H = U + p·V. That results in dH = dU + p·dV + V·dp, without non-volumentric work in dH = dq + V·dp and under constant pressure in dH = dq. If you manage to keep the pressure constant (which is quite easy in practice) the calorimetric measurement directly gives you the change of enthalpy.
 

1. Why is the concept of enthalpy important in science?

The concept of enthalpy is important in science because it helps us understand and quantify the amount of energy in a system. This is crucial in fields like thermodynamics, chemistry, and physics where energy changes are a fundamental part of understanding how systems behave.

2. How is enthalpy different from energy?

Enthalpy is a specific type of energy that is associated with the internal energy of a system. It takes into account the energy stored in the bonds between particles, as well as the energy required to change the temperature or phase of a substance. Energy, on the other hand, is a more general term that can refer to many different forms of energy, such as kinetic, potential, or thermal energy.

3. What are some real-world applications of enthalpy?

Enthalpy has many real-world applications, such as in power plants where it is used to calculate the energy output of a system, and in chemical reactions where it is used to determine the energy released or absorbed. It is also used in meteorology to understand and predict weather patterns, as well as in engineering to design more efficient systems.

4. How is enthalpy measured?

Enthalpy is typically measured using a calorimeter, which is a device that can measure the heat released or absorbed by a system. It is also often calculated using mathematical equations that take into account the different forms of energy in a system.

5. Why do we need to define enthalpy?

Defining enthalpy allows us to have a precise and quantitative understanding of energy changes in a system. It also allows us to make predictions and calculations based on this understanding, which is crucial in many scientific and engineering applications. Without a clear definition of enthalpy, it would be difficult to accurately describe and analyze energy changes in a system.

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