Enthalpy | Thermodynamics

Najam Academy
29 May 202310:55
EducationalLearning
32 Likes 10 Comments

TLDRThis educational script delves into the fundamental concepts of enthalpy and internal energy in thermodynamics. It explains that internal energy is the sum of kinetic and potential energy within a system, and cannot be measured absolutely but only in changes. For an ideal gas in an isothermal process, internal energy remains constant. Enthalpy is introduced as the heat absorbed or released, which changes the internal energy and does work on the system, calculated as ΔH = ΔU + PΔV. The script also highlights the relationship between enthalpy, the first law of thermodynamics, and provides an example to calculate the enthalpy change for a non-ideal gas.

Takeaways
  • 🔍 Internal Energy is the sum of kinetic and potential energy of all particles in a system.
  • 📉 The absolute value of internal energy cannot be determined; only changes in internal energy are measurable.
  • 🔥 Changes in internal energy can occur by altering kinetic or potential energy.
  • 🌡 For an ideal gas in an isothermal process, the internal energy remains constant, assuming no intermolecular interactions.
  • 🐘 Enthalpy is likened to a 'poor animal' that requires internal energy to perform work, representing the system's capacity to do work.
  • 🔥 Enthalpy accounts for both the change in internal energy and the work done by the system.
  • 📚 Enthalpy is defined as the heat absorbed or released by a system to cause a change, measured at constant pressure.
  • 🔄 Enthalpy change is represented by ΔH, which is the sum of the change in internal energy (ΔU) and the product of pressure and volume change (PΔV).
  • ♻️ In a cyclic process, the total change in enthalpy is zero because the system returns to its initial state.
  • 📉 Enthalpy is an extensive property, meaning its value depends on the amount of substance in the system.
  • 🔧 The relationship between enthalpy and the first law of thermodynamics is expressed as ΔH = Q at constant pressure, where Q is the heat exchanged and w is the work done by the system.
Q & A

  • What is the definition of internal energy?

    -Internal energy is the total energy of a system, which is the sum of all forms of energy of a substance, including both kinetic and potential energy.

  • Can we determine the absolute value of internal energy?

    -No, we cannot find the absolute value of internal energy. We can only determine the change in internal energy, which is the difference between the final and initial values.

  • How can the internal energy of a system be changed?

    -The internal energy of a system can be changed by altering either the kinetic energy or the potential energy of the system.

  • What is the internal energy of an ideal gas during an isothermal process?

    -For an ideal gas in an isothermal process, the internal energy is zero because there is no interaction between particles (potential energy is zero) and the temperature remains constant (kinetic energy remains constant as well).

  • What is enthalpy and how is it related to internal energy and work?

    -Enthalpy is the amount of heat absorbed or released by a system to cause a change in the system. It is related to internal energy and work as it accounts for the change in internal energy plus the work done on or by the system.

  • How is enthalpy mathematically defined in terms of internal energy and work?

    -Enthalpy change (ΔH) is mathematically defined as the change in internal energy (ΔU) plus the product of pressure (P) and volume change (ΔV), or ΔH = ΔU + PΔV.

  • What does a positive or negative enthalpy change indicate?

    -A positive enthalpy change (ΔH > 0) indicates that the process absorbs heat from the surroundings (endothermic process), while a negative enthalpy change (ΔH < 0) indicates that the process releases heat to the surroundings (exothermic process).

  • Why is enthalpy considered a state function?

    -Enthalpy is a state function because it only depends on the initial and final states of the system and is independent of the path taken to reach the final state.

  • How is the change in enthalpy related to the first law of thermodynamics?

    -The change in enthalpy (ΔH) is related to the first law of thermodynamics as it is equal to the heat absorbed at constant pressure (Q), which can be expressed as ΔH = Q at constant pressure.

  • What are the two ways to write enthalpy change at constant volume and constant pressure?

    -At constant volume, enthalpy change is written as ΔH = ΔU + VΔP, and at constant pressure, it is written as ΔH = ΔU + PΔV.

  • How is the numerical problem in the script solved to find the change in enthalpy?

    -In the given numerical problem, the change in enthalpy (ΔH) is calculated using the formula ΔH = ΔU + P2V2 - P1V1, where ΔU is the change in internal energy, and P1V1 and P2V2 are the products of pressure and volume at the initial and final states, respectively.

Outlines
00:00
🔍 Understanding Internal Energy and Enthalpy

This paragraph introduces the fundamental concepts of internal energy and enthalpy in thermodynamics. It explains that internal energy is the sum of kinetic and potential energy of particles in a system, which can be changed by altering the system's kinetic or potential energy. The paragraph also clarifies that the absolute value of internal energy cannot be determined, only its change. For an ideal gas in an isothermal process, internal energy is zero due to the lack of inter-particle interactions. Enthalpy is then defined as the heat absorbed or released by a system that is capable of doing work, and it is the sum of internal energy and the product of pressure and volume. The relationship between enthalpy and the first law of thermodynamics is established, showing that enthalpy change at constant pressure is equivalent to the heat absorbed or released.

05:02
🔧 Enthalpy Change and Its Calculation

The second paragraph delves deeper into the concept of enthalpy change, emphasizing that it is a state function dependent only on initial and final states, not the path taken. It highlights that enthalpy change is always zero in a cyclic process and is an extensive property, meaning it depends on the amount of substance involved. The paragraph also explains the two ways to express enthalpy change: at constant volume and at constant pressure. An example of a numerical problem is provided, where the change in enthalpy for a non-ideal gas undergoing a state change is calculated using the given initial and final pressures and volumes, resulting in a 76 liter atmosphere enthalpy change.

10:05
📘 Numerical Example of Enthalpy Calculation

This paragraph presents a numerical example to illustrate the calculation of enthalpy change. It provides specific values for initial and final pressures and volumes of a non-ideal gas undergoing a state change. The formula for enthalpy change, ΔH = ΔU + PΔV, is applied, and by substituting the given values, the enthalpy change for the system is determined to be 76 liter atmospheres. This example serves to reinforce the understanding of enthalpy change calculations in practical scenarios.

Mindmap
Keywords
💡Enthalpy
Enthalpy is a thermodynamic property that represents the total heat content of a system. It is defined as the sum of the internal energy of the system and the product of its pressure and volume. In the video, enthalpy is likened to 'sir denki,' a metaphorical 'animal' that uses internal energy to perform work. The script explains that enthalpy is crucial for understanding how heat changes the internal energy of a system and how it can do work, such as moving a piston in a container.
💡Internal Energy
Internal energy is the total energy contained within a system, which includes both the kinetic energy of the particles (due to their motion) and the potential energy (due to interactions between particles). The script emphasizes that internal energy is a fundamental concept for understanding enthalpy, as it is the energy that can be converted into work or heat. The video also clarifies that we can't find the absolute value of internal energy, only the change in it.
💡Kinetic Energy
Kinetic energy is the energy possessed by particles due to their motion. In the context of the video, it is one of the components of internal energy, as the gas particles in the container are in constant motion. The script explains that when heat is added to the system, the kinetic energy—and consequently the internal energy—increases.
💡Potential Energy
Potential energy is the energy resulting from the position or configuration of the particles within a system. The script mentions that gas particles possess potential energy due to their interactions with each other. However, for an ideal gas, the potential energy is considered to be zero because there is assumed to be no interaction between particles.
💡Isothermal Process
An isothermal process is a thermodynamic process in which the temperature of the system remains constant. The script explains that for an ideal gas undergoing an isothermal process, the internal energy remains zero because the kinetic energy of the particles does not change, and there is no potential energy due to the lack of particle interaction.
💡First Law of Thermodynamics
The first law of thermodynamics, also known as the law of conservation of energy, states that energy cannot be created or destroyed, only converted from one form to another. In the script, this law is related to enthalpy through the equation ΔH = ΔU + PΔV, where ΔU is the change in internal energy, P is the pressure, and ΔV is the change in volume. This law is fundamental to understanding how energy is transferred as heat (Q) and work (W) in a system.
💡State Function
A state function is a property of a system that depends only on the current state of the system, not on the path taken to reach that state. Enthalpy is described as a state function in the script, meaning that the change in enthalpy (ΔH) depends only on the initial and final states of the system, regardless of the process that occurred between them.
💡Cyclic Process
A cyclic process is one in which a system returns to its initial state after a series of changes. The script mentions that the change in enthalpy (ΔH) for a cyclic process is always zero because the system ends up in the same state it started with, implying no net change in enthalpy.
💡Extensive Property
An extensive property is a property of a system that depends on the amount of material in the system. The script explains that enthalpy is an extensive property, meaning that it varies with the size or amount of the substance in the system. More substance results in a larger change in enthalpy for the same process.
💡Endothermic Process
An endothermic process is a process in which a system absorbs heat from its surroundings. The script states that if the change in enthalpy (ΔH) is positive, the process is endothermic, indicating that heat is absorbed.
💡Exothermic Process
An exothermic process is one in which a system releases heat to its surroundings. According to the script, if the change in enthalpy (ΔH) is negative, the process is exothermic, meaning that heat is released.
Highlights

Internal energy is defined as the sum of all forms of energy of a substance, including kinetic and potential energy.

The absolute value of internal energy cannot be determined; only changes in internal energy are measurable.

Internal energy can be altered by changing the kinetic or potential energy of a system.

For an ideal gas in an isothermal process, the internal energy is zero due to lack of inter-particle interaction.

Enthalpy is introduced as a concept that includes internal energy and the capacity to do work.

Enthalpy is the heat absorbed or released by a system to effect a change, and is represented as ΔH.

The formula for enthalpy change is ΔH = ΔU + PΔV, where P is pressure and V is volume.

Enthalpy change at constant volume and pressure has specific formulations, reflecting different thermodynamic conditions.

Enthalpy is a state function, dependent only on the initial and final states, not the path taken.

In a cyclic process, the change in enthalpy (ΔH) is always zero because the initial and final states are the same.

Enthalpy is an extensive property, meaning it depends on the amount of substance involved in the process.

The relationship between enthalpy and the first law of thermodynamics is explained, showing that ΔH equals the heat exchanged at constant pressure.

The numerical problem demonstrates calculating the change in enthalpy for a non-ideal gas undergoing a state change.

The calculation of enthalpy change involves the initial and final states' pressures and volumes.

In the provided example, the enthalpy change for the system is found to be 76 liter atmospheres.

Enthalpy change is a key concept in understanding heat transfer and work done in thermodynamic processes.

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Related Tags
ThermodynamicsEnthalpyInternal EnergyKinetic EnergyPotential EnergyIdeal GasIsothermal ProcessHeat TransferFirst LawEnergy Change