Education Content Expert
Inherent Energy is defined as an energy form inherent in every substance in this universe that arises from the molecular state of motion of matter. It is symbolized by the symbol U. The unit of measurement of internal energy is the joules (J). Internal energy can vary and change with a change in temperature or a change in the state of the matter such as the change from solid to liquid or from liquid to gas.
Key Terms: Internal Energy, Intrinsic Energy, Atoms, Molecules, Ions, Joules, Kinetic Energy, Potential Energy, Motion
What is Internal Energy?
[Click Here for Sample Questions]
Internal energy is the inherent form of energy present in the system of every substance due to the substance’s state of motion.
In a well-defined body or system with proper boundaries, the total internal energy of the system is equal to the total kinetic energy created from the state of motion of the molecules, the potential energy created from the vibrational motion of the molecules and the electric energy of the atoms present within the molecules.
- The internal energy is denoted by the symbol U.
- The unit of measurement of internal energy is Joules (J).
- Internal energy is described as an extensive quantity as it is a state function of a system.
- Internal energy also comprises the energy present within the various chemical bonds.
- The internal energy in a substance can be found in various forms of energy if seen from a microscopic point of view.
Internal Energy
Specific Internal Energy
- Specific Internal Energy is the corresponding intensive thermodynamic property inherited by a substance.
- It is represented by the symbol u, which means internal energy per mass of the substance.
- The SI unit of the specific internal energy is J/g.
If the internal energy is to be expressed in the form of amount, it will be known as the molar internal energy and the SI Unit in this case would be the J/mol.
Read More:
| Internal Energy Formula | Unit of Energy | Work and Energy |
| Types of Energy | Conservation of Energy Formula | Joule's Law of Heating |
Internal Energy of a Closed System
[Click Here for Previous Years Questions]
The internal energy for a closed system will be given as
ΔU = q + W
Where
The internal energy appears as heat if an energy exchange occurs because of the temperature difference between a system and its surroundings, else, it appears as work. The energy is transferred as work when a force acts on a system through a distance. As per the above-mentioned equation, the energy is conserved.
Components of Internal Energy in a System
[Click Here for Sample Questions]
The components of internal energy are as follows:
- Thermal Energy: It has two sub-parts:
- Sensible Heat- It is the energy change of a system associated with molecular translation, rotation, vibration; electron translation and spin; nuclear spin of molecules.
- Latent Heat- It is the energy released or required for a change from liquid to vapour phase that requires heat of vaporization.
- Chemical Energy: It is the energy that is associated with the chemical bonds in a molecule.
- Nuclear Energy: It is the huge amount of energy released associated with the bonds within the nucleus of the atom.
Components of Internal Energy
Given below are the physical and chemical processes that have an impact or change on the internal energy of a system.
Transferring Energy across System Boundary
- Heat Transfer: It refers to the energy transfer from a high temperature to a low-temperature state.
- Work Transfer: It refers to the energy transfer driven by changes in the physical properties of a system.
- Mass Transfer: It refers to the energy transfer by mass flowing across a system boundary.
Change via internal Processes
- Mixing: On mixing of the components, the heat released might lead to lower internal energy.
- Chemical Reaction: The heat that is required or released during a chemical reaction that changes chemical energy.
- Nuclear Reaction: The heat released during a nuclear reaction that changes nuclear energy.
Read More: Thermodynamics Important Questions
Change in Internal Energy
[Click Here for Previous Years Questions]
The change in the internal energy means nothing but the difference in the internal energies of the two different states during a chemical reaction.
For example, let EA be the initial energy in state A and EB be the initial energy in state B. Therefore, the difference between the initial energies in the two states will be,
ΔU = EA - EB
This difference in the two states of A and B is a fixed quantity and will be independent of the respective resultant path taken by both A and B.
As for the chemical reaction that takes place, the change in the internal energy may be considered as the difference between the internal energies of the products and that of the reactants. This can be represented as
ΔU = Eproducts – Ereactants
Where
- E(products) = internal energy of the products
- E(reactants) = internal energy of the reactants
This implies that the internal energy is only and only dependent on the initial and the final state of the substance and independent of the path. This signifies that the internal energy is a state function which means that the value of change in internal function will remain the same even if the change is brought in a different manner.
Read More:
| Thermodynamic Processes | First Law of Thermodynamics | Applications of Thermodynamics |
| Zeroth Law of Thermodynamics | Second Law of Thermodynamics | Third Law of Thermodynamics |
Solved ExampleExample: When 0.5g of benzoic acid (molecular mass = 122) is burnt in excess of oxygen in a bomb calorimeter, the heat evolved is 3150 cal at 25oC. What will be ΔU for the reaction? C6H5COOH(s) + 7.5O2(g) → 7CO2(g) + 3H2O(l) R = 1.987 K cal-1K-1 Solution: The heat evolved while burning 1 mol (122g) of benzoic acid at a constant volume will be = -3150 cal x (122 g/mol/0.5 g) = -768,600 cal/mol Thus, ΔU = -768.6 Kcal mol-1 |
Read More: MCQs on Thermodynamics
Things to Remember
- Internal Energy is inherent energy that is present inside every substance and is an extensive property.
- It is symbolized by U and its unit of measurement is joules (J).
- Intrinsic energy is made up of kinetic energy, potential energy and electrical energy of the atoms present within.
- Change in the internal energy means the difference in the internal energies of the two different states during a chemical reaction.
- The value of change in internal function will remain the same even if the change is brought in a different manner.
Previous Year’s Questions (PYQs)
- Internal energy is the sum of…
- Internal energy does not include…
- Internal energy and pressure of a gas per unit vol… (NEET 1993)
- Internal energy of gas remains unchanged in…
- The internal energy of one mole of an ideal gas is…
- Which of the following thermodynamic relation is…
- In a cyclic process the change in the internal energy… (JKCET 2015)
- One mole of an ideal gas undergoes a cyclic process…
- According to the first law of thermodynamics
- Which of the following laws of thermodynamics form… (JKCET 2012)
- Thermodynamic properties are divided into two broad…
- The state of a thermodynamic system is represented… (BCECE 2010)
Sample Questions
Ques. What do you mean by the internal energy of a system? [3 Marks]
Ans. The internal energy of the system is equal to the total of the kinetic energy created from the state of motion of the molecules, the potential energy created from the vibrational motion of the molecules and the electric energy of the atoms present within the molecules.
Ques. Can a ship on the surface of seawater use the internal energy of the seawater to operate its engine? Explain your answer with reasons. [3 Marks]
Ans. For a ship to use the internal energy of the seawater to operate its own engine, the internal energy of the seawater has to be converted into mechanical energy and to convert the internal energy to mechanical energy, a sink of heat is required at a temperature lower than the temperature of seawater and also having high internal capacity. Since no such sink is available in the seawater, a ship cannot use the internal energy of the sea to operate its engines.
Ques. What happens to a particular system when a certain amount of work is done by the system in a process and in which no heat is transferred to or from the system? Do the internal energy and the temperature of the system change or not and how? [3 Marks]
Ans. Yes, when a certain amount of work is done by the system in a process and in which no heat is transferred to or from the system, the internal energy and the temperature of the system change. Since the system is performing some work and no heat is allowed to transfer to or from the system, the temperature of the system gradually decreases. And as the temperature decreases, as a result, the internal energy of the system also decreases simultaneously.
Ques. Does every substance possess internal energy? [3 Marks]
Ans. Each and every substance present in this universe possesses a given fixed amount of internal energy which is dependent on the substance's chemical nature and its state of existence in the environment. This energy is known as the intrinsic energy and the fixed amount of internal energy of the substance is in fact equal to all the various forms of energies present within all the atoms, molecules and ions forming part of the substance's constituents.
Ques. Why is the Cp of a gaseous substance always greater than the Cv of the gas? [3 Marks]
Ans. When a gaseous substance is exposed to heat with the volume of the gas remaining constant, the internal or more particularly, the kinetic energy of the system is made to increase. Thereby increasing the system’s temperature. But when gas is to be heated at a pressure that is constant in value, then an additional amount of heat is required to increase the temperature of the system, along with that, the volume of the system and the internal energy of the system is also increased.
Therefore, according to the definition, the Cp of a gaseous substance is always greater than the Cv of the gas.
Ques. Why is it that although the mechanical energy of a system can be fully converted into heat energy, the reverse is not true? [3 Marks]
Ans. It is true that although the mechanical energy of a system can be fully converted into heat energy, heat energy can never be completely converted to mechanical energy.
This is due to the fact that the entirety of the mechanical energy can be absorbed by the molecules of the given system in the form of their kinetic energy and this kinetic energy subsequently gets converted into heat energy. But in the case of heat energy, the entirety of the heat energy cannot be converted into work as a part of it is always retained by the system as its internal energy.
Ques. What are the factors that affect the internal energy of a system? [3 Marks]
Ans. The internal energy of a system can be changed by altering the substance’s volume or its temperature without changing the number of particles present in the interior of the object.
If the temperature of a system is increased, it will result in the molecules present inside the system moving faster, and thus the kinetic energy will increase resulting in more internal energy. And since the temperature is related to pressure and volume, by instilling a change in the pressure and the volume of the system, we can also change the Internal energy of the system.
Ques. What is a state function? Explain if the internal energy of a system is a state function or not. [3 Marks]
Ans. A state function of a system is defined as a property of a system whose value depends on the initial and the final state of the system and not on the path by which the mentioned state is achieved.
And as discussed earlier, the internal energy of a substance is only and only dependent on the initial and the final state of the substance and is completely independent of the path by which the state is obtained. Thus, the internal energy is a state function.
Check-Out:
Comments