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Isobaric Process is a thermodynamic process that takes place at constant pressure. Isobaric is derived from the Greek “Iso” and “Baros”, meaning “Equal Pressure”. As a result, when the volume is extended or reduced, constant pressure is obtained. This effectively cancels out any pressure changes caused by heat transmission.
When heat is delivered to a system in an isobaric process, some work is done. There is, however, a change in the system's internal energy. As a result, no quantities, as defined by the first rule of thermodynamics, become zero. Isobaric process is also known as Constant Pressure Process.
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Keyterms: Thermodynamics, Constant Pressure Process, internal energy, force, piston
How Isobaric Process is Achieved?
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Isobaric Process is conducted under Constant Pressure. The process to maintain Constant Pressure can be explained via a simulation.
A gas cylinder contains a tight-fitting, massless piston that can slide up and down. The cylinder is sealed, preventing atoms from entering or escaping. A mass on top of the piston exerts constant downward force Mg. The piston is also pressed down by the atmosphere. The upward force PA exerted on the piston by the gas in the cylinder, where A denotes the piston's area, perfectly balances the downward force.
Isobaric Process
This pressure is independent of the gas's temperature or the piston's height, hence it remains constant as long as M remains constant.
Isobaric Process
When the gas in the cylinder warms up, it expands and pushes the piston upward. However, the pressure, which is governed by mass M, will remain constant. The horizontal line 1→ 2 on the P – V diagram represents this process. This is referred to as an isobaric expansion. If the gas is cooled, isobaric compression occurs, lowering the piston. On a P – V diagram, an isobaric process appears as a horizontal line.
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Isobaric Process: Examples
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The boiling of water leading to steam formation or the freezing of water leading to formation of ice are examples of isobaric processes. A gas expands or contracts to maintain constant pressure during the operation, resulting in a net amount of work done by or on the system. The amount of heat dQ is used in part to raise the temperature dT and in part to perform external work.
\(dQ =CpdT + P dV\)
Work Done by a Gas in an Isobaric Process
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The work done is calculated using the equation;
\(W = \int\limits_{V_f}^{V_i} P dV\)
because the pressure in an isobaric process is constant, the integral becomes
\(W = P_i \int\limits_{V_i}^{V_f} = P_i(V_f - V_i) = P_i\Delta V\)
If the gas expands, Vf >Vi so ΔV > 0 and the work done by the gas is positive.
When the gas is compressed, Vf <Vi so that ΔV < 0, and the work that is done by the gas is negative.
Work Done by a Gas in an Isobaric Process
The rectangular region under the isobaric path on the P-V diagram represents the work performed by the gas. The area is either positive or negative depending on whether the gas expands or contracts.
What is Thermodynamic Process?
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A Thermodynamic Process is one where the system undergoes a change in energy. This results in changes in its physical properties such as Pressure, Volume, Internal Energy, Temperature, Heat Transfer, etc. When all of the system's macroscopic physical attributes return to their original values, the system returns to its original state.
Work and heat transfer are two processes that alter the thermodynamic equilibrium state. A quasi-static process occurs when a system changes slowly enough that each successive state it passes through is effectively in equilibrium. The reversible processes are all quasi-static in nature; they occur very slowly. Equilibrium state is a static state. In a Reversible Process, the system does not deviate from equilibrium, and even if it does, it does so in extremely small amounts.
Equilibrium thermodynamics consist of other thermodynamic processes as well. Those processes are indicative of the constant thermodynamic variable.
- Isothermal Process: Temperature of the System is kept constant.
- Isochoric Process: Volume of the System is kept constant.
- Adiabatic Process: No Heat is transferred to or from the system.
First Law of Thermodynamics in Isobaric Process
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The heat given per mole per unit rise in the temperature of a gas is known as molar heat capacity at constant pressure and is written by Cp = (ΔQ/nΔT)p, where the subscript ‘p' signifies constant pressure.
As previously stated, the heat given to the gas in an isobaric process is used to increase its internal energy by increasing its volume by a little amount (dV) (dU).
From the First Law of Thermodynamics ΔQ = ΔU + ΔW, we get
(dQ)p = dU + PdV……. (i)
(at constant volume dV = 0, therefore W=0, from the first law of thermodynamics ΔQ = ΔU or heat supplied at constant volume = change in its internal energy). So, dU = (dQ)v.
Therefore equation becomes,
(dQ)p = (dQ)v + PdV……. (ii)
For an Ideal Gas, PV = nRT, Therefore,
PdV = nRdT,
(dQ)p = (dQ)v + nRdT……. (iii)
Dividing (iii) by ndT we get
(dQ/ndT)p = (dQ/ndT)v + (nRdT/ndT)
(dQ/ndT)p = Cp.
Similarly, (dQ/ndT)v = Cv.
By putting these values, we get
Cp = Cv + R.
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Things to Remember
- Isobaric Process is a thermodynamic process that takes place at constant pressure.
- Constant Pressure is obtained when the volume is extended or reduced. This effectively cancels out any pressure changes caused by heat transmission.
- Isobaric process is also known as Constant Pressure Process.
- The boiling of water leading to steam formation or the freezing of water leading to formation of ice are examples of isobaric processes.
- A Thermodynamic Process is one where the system undergoes a change in energy.
- Work and heat transfer are two processes that alter the thermodynamic equilibrium state.
- The heat given per mole per unit rise in the temperature of a gas is known as molar heat capacity at constant pressure and is written by Cp = (ΔQ/nΔT)p, where the subscript ‘p' signifies constant pressure.
Previous years Questions
- A Carnot engine is operating between a hot body and cold body maintained at temperature T1T1 and T2T2 respectively.
- If the amount of heat given to a system is 35J and the amount of work done on the system is 15J, then the change in internal energy of the system is
- When you make ice cubes, the entropy of water
- The value of internal energy change for the above reaction at this temperature will be
- A heat engine absorbs heat Q1Q1 at temperature T1T1 and heat Q2Q2 at temperature T2T2. Work done by the engine is (Q1+Q2)(Q1+Q2). This data
- The value of enthalpy of formation of OH−OH− ion at 25oC25oC is :
- Which of the following is a characteristic of a reversible reaction?
- What is the net change in the internal energy of the system?
- The final energy of the system will be
- A well stoppered thermos flask contains some icecubes. This is an example of
- Which of the following is not a correct expression?
- Adiabatic expansions of an ideal gas is accompanied by
- All naturally occurring processes proceed spontaneously in a direction which leads to
- Ammonium chloride when dissolved in water leads to a cooling sensation. The dissolution of ammonium chloride at constant temperature is accompanied by
- During free expansion, external pressure is always less than the pressure of the system.
- BaSO4 is insoluble in water due to its
- Bond dissociation energy of O2(g)isxkJmol−1. This means that
- Cv values for monoatomic and diatomic gases respectively are
- ΔH for the reaction, OF2+H2O→O2+2HF (B.E. of $O ?
- ΔU?ΔU? of combustion of CH4(g)CH4(g) at certain temperature is −393kJmol−1−393kJmol−1. The value of ΔH?ΔH? is
Sample Questions
Ques. What exactly does an isobaric process entail? (1 mark)
Ans. In an isobaric process, the gas's work on the environment reduces the gas's internal energy and temperature. As a result, the total amount of heat injected into the gas raises the gas's internal energy and temperature.
Ques. How do the Isobaric and Isochoric Processes differ? (1 mark)
Ans. An isochoric process takes place in a thermodynamic system with a constant volume, whereas an isobaric process takes place in a thermodynamic system with constant pressure.
Ques. Explain any example of the Isobaric process. (1 mark)
Ans. Boiling water is an example of an isobaric process. The resulting steam expands to nearly 1600 times its original volume as the water boils while remaining under constant atmospheric pressure. Isobaric processes include the transformation of water to ice or freezing.
Ques. When is work done maximum in the isobaric process? (1 mark)
Ans. When the external pressure of the environment on the system equals P, the system's pressure, the maximum work is done. If V is the system's volume, the work done as the system transitions from state 1 to state 2 during an isobaric thermodynamic process is maximum.
Ques. Are isobaric processes irreversible? (1 mark)
Ans. Isobaric processes are mostly reversible because work done is related to volume rather than pressure, which is constant in isobaric processes. However, this assertion is not always true. As a result, there is an irreversible isobaric process.
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