There is no exchange of heat between the system and the surroundings in the adiabatic process which is an integral part of thermodynamics. The concept of adiabatic process is a fundamental principle in physics which deals with the behavior of gases.
By understanding the concept of the adiabatic process, students get an idea about work, heat, and internal energy. This article provides insight on important topics like what is an adiabatic process, work done by adiabatic process derivation, daily life examples of adiabatic process, adiabatic expansion, and compression, and types of adiabatic processes.
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Define adiabatic process: There is no heat exchange in an adiabatic process in thermodynamics, neither during an adiabatic expansion nor compression. An adiabatic process is one in which, both irreversibility and reversibility are possible. The following conditions must be met for an adiabatic reaction to occur:
Insulation must be perfect between the system and its surroundings. It is important to carry out the process rapidly. The turbines are great examples of adiabatic systems. During the adiabatic process, the work done changes internal energy.
If
If
In terms of adiabatic processes, the following equation applies:
where,
According to the first law of thermodynamics,
For adiabatic process,
Let W work be done as the system goes from initial state
Work Done,
Using the adiabatic process formula,
By integrating both sides
We know that, constant
Simplifying we get,
Using ideal gas,
Substituting in (2), we get
where,
This is the work done by the adiabatic process equation.
Adiabatic compression causes a gas to increase in temperature, while adiabatic expansion, or a spring, causes the temperature to drop. An ideal gas, however, expands with isothermal heat.
In many practical situations, heat conduction through walls can be slow compared to the compression time of gas, because a piston compressing a gas contained inside a cylinder increases its pressure.
Generally, diesel engines make use of this to ignite the fuel vapor when there is little heat dissipation during an adiabatic process a compression stroke.
An adiabatically isolated system is cooled by decreasing the pressure on it, which allows it to expand and change its environment.
(i) Reversible Adiabatic Process
(ii) Irreversible Adiabatic Process
The area under the PV diagram of the adiabatic process gives the work done by the adiabatic process. The curve of the adiabatic process is steeper than that of the isothermal process.
Example of adiabatic processes include:
The isothermal versus adiabatic process is explained in the table below:
Isothermal process |
Adiabatic process |
An isothermal process is defined as one of the thermodynamic processes which occur at constant temperature. |
An adiabatic process is defined as one of the thermodynamic processes that occur without any heat transfer between the system and the surroundings. |
Work done in an adiabatic process is due to the change in the net heat content in the system. |
Work done in the adiabatic process is due to the change in its internal energy. |
The temperature cannot be varied |
The temperature can be varied |
There is a transfer of heat |
There is no transfer of heat |
Example 1: The work of 146 kJ is performed to compress one kilomole of gas adiabatically and in this process, the temperature of the gas increases by
1) monoatomic
2) diatomic
3) triatomic
4) a mixture of monoatomic and diatomic.
Solution:
Adiabatic Process
When a Thermodynamic System changes in such a way that no exchange of heat takes place.
1. Work Done Formula:
2. Plug in Values:
3. Compute Numerator:
4. Solve for
5. Find
Therefore, the corrected value of
Hence, the answer is the option (2).
Example 2: When a gas expands adiabatically
1) The system should allowed to expand slowly
2) Internal energy of gas is used in doing work
3) The law of conservation of energy does not hold
4) No energy is required for expansion
Solution:
1. No Heat Exchange: In an adiabatic process, there should be no exchange of heat between the system and surroundings, meaning
2. Sudden Compression or Expansion: For a process to be approximately adiabatic, it should occur quickly. This rapid change ensures that there is no time for heat to transfer, as in the case of a sudden burst of a tire.
Since
or
This means that if
Example 3: A given system undergoes a change in which the work done by the system equals the decrease in its internal energy. The system must have undergone an
1) Isothermal change
2) Adiabatic change
Solution:
In an adiabatic process:
According to the first law of thermodynamics:
For an adiabatic process, there is no exchange of heat between the system and its surroundings.
So,
This means the work done by the system equals the decrease in internal energy.
Hence, the answer is option 2.
Example 4: During an adiabatic process, the pressure of a gas is found to be proportional to the cube of its absolute temperature. The ratio CP/CV for the gas is
1)
2) 2
3)
4)
Solution:
or
From the adiabatic equation:
Using equations (1) and (2), we can equate the powers of
Solving this, we get:
or
Thus,
Hence, the answer is option (4).
Example 5: Two moles of an ideal monoatomic gas occupy a volume V at
Calculate (a) the final temperature of the gas and (b) the change in its internal energy.
Solution:
The equation of state for an adiabatic process is given by:
On solving this, we find:
For an adiabatic process, the relationship between temperature and volume is:
Given
or
Next, calculating the change in internal energy
This simplifies to:
Hence, the answer is the option 4.
As a thermodynamic process, Adiabatic processes are reversible adiabatic process, processes with constant entropy for an ideal gas. An adiabatic process is represented mathematically by ΔQ=0
A closed system with constant pressure and diminishing temperature exhibits an ideal behaviour known as adiabatically expanding.
In addition, the air under adiabatic compression does not lose or gain heat, cause its internal energy to be increased, and therefore the external work done in adiabatic process on the air is equal to the internal work carried out on it. Since the temperature rises during an adiabatic process compression, the pressure of air is greater than the volume.
When an adiabatic process occurs, the entire system's heat remains constant.
Gases under high pressure undergo chemical changes when they explode in a cylinder.
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