A gas may be taken from one thermodynamics state to the other through many different processes. some of the discussed below.
Isobaric process: - “The process during which pressure of the system remains constant is called isobaric process.”
The thermodynamic equilibrium state of a system keeps changing during such a process and its P → V graph
is a straight line parallel to the V-axis.
Isochoric process: - Volume of a system remains constant during this process. As Δ V = 0,
work, W = P Δ V = 0. Since no work is done, Q = Δ U from the first law of thermodynamics.
Adiabatic process: - No heat exchange occurs between a system and its environment in this process. This happens when either the system is thermally insulated or is very rapid. As Δ Q = 0 in the adiabatic process, ΔU = - W from the first law of thermodynamics.
Isothermal process: - “A thermodynamic process during which temperature of a system remains constant is called an isothermal process.”
Cyclic process: “A thermodynamic process in which system undergoes a series of processes starting from some thermodynamic equilibrium state and finally returns to the original thermodynamic state is called a cyclic process.”
In a cyclic process, there is no change in the internal energy of the system ( i.e., ΔU = 0 ) as the initial and final states are the same. Hence, Q = W from the first law of thermodynamics. Thus, the net amount of heat absorbed by the system is equal to the net amount of work done by the system at the end of the cyclic process.
Reversible and irreversible processes: - If a gas in the cylinder in equilibrium with the environment at temperature T is quickly compressed to half its volume and then allowed to come in equilibrium with the environment back to temperature T, it passes through many inequilibrium states in the process. If it is
now allowed to return quickly to its original volume, and allowed to return to the thermal equilibrium with the environment, it would not pass through the same intermediate states as earlier. Such processes are irreversible processes, e.g., rusting of iron, erosion of rocks, growing of a man, etc. are irreversible processes. Now, consider another type of process. The volume of the gas is made half by several differential decreases of volume made very slowly. Differential decrease in volume results in differential increase of temperature, but the process being slow, the system has sufficient time to give up the excess heat to the environment regaining its temperature and returning to the equilibrium state. Thus, in this process, the system passes through the equilibrium states and the temperature remains constant. Such a process can be reversed by differential increase in volume on the same path of equilibrium states. This is the example of a reversible isothermal process. Here, piston was assumed to be frictionless. A reversible
process is one that, by a differential change in the environment, can be made to retrace its path.
Isobaric process: - “The process during which pressure of the system remains constant is called isobaric process.”
The thermodynamic equilibrium state of a system keeps changing during such a process and its P → V graph
is a straight line parallel to the V-axis.
Isochoric process: - Volume of a system remains constant during this process. As Δ V = 0,
work, W = P Δ V = 0. Since no work is done, Q = Δ U from the first law of thermodynamics.
Adiabatic process: - No heat exchange occurs between a system and its environment in this process. This happens when either the system is thermally insulated or is very rapid. As Δ Q = 0 in the adiabatic process, ΔU = - W from the first law of thermodynamics.
Isothermal process: - “A thermodynamic process during which temperature of a system remains constant is called an isothermal process.”
Cyclic process: “A thermodynamic process in which system undergoes a series of processes starting from some thermodynamic equilibrium state and finally returns to the original thermodynamic state is called a cyclic process.”
In a cyclic process, there is no change in the internal energy of the system ( i.e., ΔU = 0 ) as the initial and final states are the same. Hence, Q = W from the first law of thermodynamics. Thus, the net amount of heat absorbed by the system is equal to the net amount of work done by the system at the end of the cyclic process.
Reversible and irreversible processes: - If a gas in the cylinder in equilibrium with the environment at temperature T is quickly compressed to half its volume and then allowed to come in equilibrium with the environment back to temperature T, it passes through many inequilibrium states in the process. If it is
now allowed to return quickly to its original volume, and allowed to return to the thermal equilibrium with the environment, it would not pass through the same intermediate states as earlier. Such processes are irreversible processes, e.g., rusting of iron, erosion of rocks, growing of a man, etc. are irreversible processes. Now, consider another type of process. The volume of the gas is made half by several differential decreases of volume made very slowly. Differential decrease in volume results in differential increase of temperature, but the process being slow, the system has sufficient time to give up the excess heat to the environment regaining its temperature and returning to the equilibrium state. Thus, in this process, the system passes through the equilibrium states and the temperature remains constant. Such a process can be reversed by differential increase in volume on the same path of equilibrium states. This is the example of a reversible isothermal process. Here, piston was assumed to be frictionless. A reversible
process is one that, by a differential change in the environment, can be made to retrace its path.
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