Learn about thermodynamic processes and systems. Review the definition, explanations, and examples of isobaric, isochoric, isothermal, and adiabatic processes.
Updated: 03/31/2022
Isobaric, Isochoric, Isothermal & Adiabatic Processes
Thermodynamic Process
Thermodynamics is the study of energy transfers in a system, understood through the parameters of heat, work, and temperature. Consider this relatable example: You fill a bathtub with hot water and climb in. Initially, because the water temperature is greater than your body temperature, the bath feels comfortable and warm. Gradually, the heat from the water transfers to your body and the bath begins to cool until it reaches body temperature. Because it is not a closed system, the water will continue to cool as it loses heat to the air until the bathtub is uncomfortably cool and you decide to get out.
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Thermodynamic Systems
When discussing thermodynamics, a system refers to the objects being examined and the surroundings refer to everything else. In the bathtub example the system refers to the bathtub, including the water and the individual in it. The surroundings include the bathroom and everything in it, including the air. There are three different types of thermodynamic systems: open, closed, and isolated.
An open system refers to a system in which matter and energy are transferred between it and the surroundings. For example, a pot of boiling water on the stove with the lid off is an open system. Both heat and water vapor may transfer from the pot to the stove or the surrounding atmosphere.
A closed system refers to a system in which only energy is transferred between it and the surroundings. If you place a lid on top of the pot of boiling water it becomes a closed system. Heat may still be lost to the stove and the atmosphere but no water vapor, or matter, can leave.
An isolated system refers to a system where neither matter nor energy are transferred between it and the surroundings. A covered thermos full of hot water is an example of an isolated system. Since a thermos is designed to retain heat, heat and water vapor are not lost to its surroundings. Isolated systems are often the most useful since environmental factors can be largely ignored. However, there are no truly isolated systems.
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Four Types of Thermodynamic Processes
Thermodynamic processes are the transfers of energy, in the form of heat, between or within a system. There are four different types of thermodynamic processes: isobaric, isochoric, isothermal, and adiabatic.
Isobaric
An isobaric process is a process in which the pressure in the system remains constant. It is derived from the Greek words isos, meaning constant, and baros, meaning pressure. Pressure is the force of the molecules exerted against the walls of the system, the chamber. Temperature is proportional to the speed of the molecules within the system.
Consider a closed system chamber of gas with a movable piston controlling the volume. In an isobaric system, increasing the temperature of the gas expands the gas, therefore expanding the overall volume of the system. Because the piston allows the volume of the system to change with temperature, the pressure will remain constant.
In an isobaric process, the work done on the system is found using the following equation:
{eq}W = Pi*dV {/eq}
{eq}W {/eq} refers to the work done on the system, {eq}Pi {/eq} refers to the initial pressure of the system, and {eq}dV {/eq} refers to the change in the volume of the system.
Isochoric
An isochoric process is a process in which the volume of the system remains the same. It is derived from the Greek words isos and khora, meaning space.
Consider the same closed system chamber of gas this time without the movable piston. As gas molecules expand, they exert more and more force against the walls of the chamber. Since the volume of the container remains constant, increasing the temperature of the gas will increase the pressure of the system.
In an isochoric process, change in pressure or temperature of the system is found using the following equation:
{eq}P1/T1 = P2/T2 {/eq}
{eq}P1 {/eq} refers to the initial pressure and {eq}P2 {/eq} refers to the final pressure. {eq}T1 {/eq} refers to the initial temperature and {eq}T2 {/eq} refers to the final temperature.
Isothermal
An isothermal process is a process in which the temperature of the system remains constant. It is derived from the Greek words isos and therme, meaning heat. In this process, heat energy is transferred so slowly that thermal equilibrium is maintained.
This time, consider again the uncovered pot of boiling water. Once boiling, although constant heat is being applied to the system, the temperature of the water will remain the same. This is due to the fact that excess energy is also able to be transferred to the surroundings (the atmosphere). In an isothermal process, when work is done on a system there must be a release of heat energy from the system to its surroundings.
In an isothermal process, change in pressure and volume of the system is found using the following equation:
{eq}P1V1=P2V2 {/eq}
{eq}P1 {/eq} refers to the initial pressure and {eq}P2 {/eq} refers to the final pressure. {eq}T1 {/eq} refers to the initial temperature and {eq}T2 {/eq} refers to the final temperature.
Adiabatic
An adiabatic process is a process in which no heat energy is transferred out of the system. Unlike an isothermal process, in which heat energy is transferred out of the system to maintain a constant temperature, adiabatic processes occur in insulated environments, prevent the transfer of heat energy, and result in a change in the temperature of the system.
An example of such a process would be an insulated chamber of gas with a movable piston. Lowering the piston to decrease the volume would increase the pressure and temperature of the system. Raising the piston to increase the volume would decrease the pressure and temperature. In order for this to occur, the system must be completely insulated or the work done on the system must be done at very high speed.
The equation for the adiabatic process is:
{eq}PVy = constant {/eq}
Where P refers to pressure, V refers to volume, and {eq}y {/eq} refers to the ratio of heat capacity, or amount of heat required to change the system one temperature unit, at constant pressure to heat capacity at constant volume.
Lesson Summary
Thermodynamics refers to energy transfers in a system, understood through the parameters of heat, work, and temperature. There are three different types of thermodynamic systems: open, closed, and isolated. In an open system, energy and matter are freely transferred between it and the surroundings. In a closed system, only energy is transferred. In an isolated system, no energy or matter are transferred between the system and its surroundings.
There are four types of thermodynamic processes: isobaric, isochoric, isothermal, and adiabatic. In each process, one variable remains constant. When work is applied in an isobaric process, pressure remains constant as volume and temperature change. In an isochoric process, volume remains constant as pressure and temperature change. When work is applied in an isothermal process, temperature within the system remains constant as pressure and volume change. This is made possible due to a loss of heat energy from the system. In an adiabatic process, temperature, pressure, and volume change when work is done on the system. Adiabatic processes can only occur in a perfectly insulated system or at high speeds.
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- FAQs
Categorizing Real-Life Systems
The following situations might be described (or well approximated) as one of the 4 types of thermodynamic systems. Choose the correct one (if any).
- You let bread rise on the counter.
- A sealed cooler of dry ice evaporates.
- You boil water in a pressure cooker.
- Oxygen is carried from your lungs to cells in your blood vessels.
- A bag of chips deflates in cold weather.
Answers
- Bread rising on the counter happens at constant pressure (atmospheric pressure), so it is isobaric. Notice how the volume changes which is common in constant pressure systems.
- A sealed cooler is about as close as we can get to an insulated system in everyday life. No heat is exchanged, so the evaporation is happening under adiabatic conditions.
- In a pressure cooker, the pressure increases with temperature, but the vessel is made so that the volume is constant. This is isochoric.
- As warm-blooded animals, our bodies do their best to maintain a constant temperature, so most of the processes in our bodies are taking place under approximately isothermal conditions.
- The bag of chips deflating corresponds to none of the described thermodynamic conditions. It is not well insulated, so heat is exchanged, the temperature is also changing because the outside temperature changing. Both the pressure and volume are being reduced.
What is meant by isobaric process?
An isobaric process is a thermodynamic process that occurs in a system at constant pressure. The amount of work is found by multiplying the initial pressure and the change in volume of the system.
What are different types of thermodynamic process?
The four different types of thermodynamic processes. Isobaric processes occur at constant pressure. Isochoric processes occur at constant volume. Isothermal processes occur at constant temperature. Adiabatic processes involve no transfer of heat energy.
Which are in isochoric process?
An isochoric process is a thermodynamic process in which the volume of the system remains constant. In it, the ratios of temperature and pressure remain constant.
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Thermodynamic Processes | Isobaric, Isochoric, Isothermal & Adiabatic
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