A thermodynamic process refers to the transformation of a system’s state variables, such as pressure, volume, and temperature. It’s a fundamental concept in thermodynamics that helps describe energy transfer and work done on or by a system.

Both Isochoric and isobaric concepts are used in thermodynamics. An isochoric process, also known as an isovolumetric or constant volume process, occurs when the volume of a system remains constant. In this process, work is done only by pressure changes, and there is no change in volume. While, an isobaric process takes place under constant pressure conditions, meaning the pressure remains the same. It often involves changes in volume and temperature while work is done on or by the system.

isochoric vs isobaric process

These are the differences between isochoric and isobaric processes below:

Isochoric Process Isobaric Process
Isochoric processes to maintain a constant volume throughout, with no change in the system's volume (∆V = 0). Isobaric processes keep the pressure constant while allowing changes in volume and temperature.
In isochoric processes, no mechanical work is performed as ∆V = 0, so work done is zero (W = 0). Isobaric processes involve work, with work done calculated as W = P∆V, considering the change in volume.
Pressure may change in isochoric processes, depending on temperature changes, but volume remains constant. Pressure is held constant in isobaric processes, allowing volume and temperature to vary.
The ideal gas law (PV = nRT) is applicable to isochoric processes but simplifies to P1/T1 = P2/T2 due to constant volume. The ideal gas law (PV = nRT) applies to isobaric processes, simplifying to V1/T1 = V2/T2 with constant pressure.
Heat transfer can occur in isochoric processes, leading to temperature changes while maintaining constant volume. Heat transfer is possible in isobaric processes, influencing temperature changes at constant pressure.
These processes are used in calorimetry, bomb calorimeters, and material testing under constant volume conditions. These processes find applications in heat exchangers, chemical reactions at constant pressure, and power plants.
Isochoric processes are common in the study of closed chemical reactions, ideal for investigating heat effects. Isobaric conditions are suitable for open chemical reactions, allowing for reactions involving gases and liquids.
A classic example of an isochoric process is the operation of a bomb calorimeter during combustion experiments. An example of an isobaric process is the expansion of a gas in a piston-cylinder system under constant pressure.
Isochoric processes provide insight into how substances behave under conditions of constant volume. Isobaric processes help understand how materials and gases behave at constant pressure.
These processes demonstrate that work is not involved, focusing on heat transfer and energy changes at constant volume. These processes involve both work and heat interactions, illustrating how energy changes occur at constant pressure.

Isochoric Process: Understanding Constant Volume Processes

An isochoric process is characterized by the maintenance of a constant volume throughout the process. This implies that any energy interactions, such as heat transfer, can lead to changes in other properties like temperature and pressure, but they do not result in any changes in the system’s volume.

Equation of State

In the context of ideal gases, the ideal gas law (PV = nRT) still applies to isochoric processes. However, since volume (V) is constant, the equation simplifies to P1/T1 = P2/T2, where P1 and T1 are the initial pressure and temperature, and P2 and T2 are the final pressure and temperature.

Work Done

The work done during an isochoric process is zero (W = 0). This is because work is defined as the product of pressure and change in volume (W = P∆V), and with ∆V equal to zero, no work is done in changing the volume.

Heat Transfer

Heat transfer can still occur in an isochoric process. If heat is added to the system, its internal energy will increase, leading to a rise in temperature. Conversely, if heat is removed, the temperature will decrease.


One common example of an isochoric process is the operation of a bomb calorimeter in calorimetry. In a bomb calorimeter, a chemical reaction takes place inside a rigid container, and the volume remains constant. This allows scientists to measure the heat of the combustion of a substance.

Isobaric Process: Understanding Constant Pressure Processes

An isobaric process is characterized by the constancy of pressure. This means that the pressure within the system does not change during the process. Isobaric processes are commonly encountered in various real-world scenarios, making them a valuable concept in thermodynamics.

Equation of State

The ideal gas law (PV = nRT) is often used in the context of isobaric processes. Since pressure (P) is constant, the equation simplifies to V1/T1 = V2/T2, where V1 and T1 are the initial volume and temperature, and V2 and T2 are the final volume and temperature.

Work Done

Work is done in an isobaric process when the volume of the system changes. The work (W) done during an isobaric process is calculated as W = P∆V, where P is the constant pressure, and ∆V is the change in volume. Work can be done on the system (compression) or by the system (expansion) depending on the direction of the volume change.

Heat Transfer

Heat transfer may also occur during an isobaric process, leading to changes in temperature. If heat is added, the temperature increases, and if heat is removed, the temperature decreases, all while maintaining the constant pressure.


Isobaric processes are commonly observed in a wide range of scenarios. For instance, the operation of a piston cylinder system with constant external pressure is an example of an isobaric process. Many industrial processes, such as steam generation in boilers, occur under isobaric conditions, where pressure is controlled to ensure efficient operation.


Isochoric Processes

  • Isochoric processes are crucial in calorimetry, where the heat of a chemical reaction can be measured under constant volume conditions. Bomb calorimeters, for example, use isochoric chambers to determine the heat of combustion of substances.
  • In acoustics, the behavior of sound waves in a closed, constant volume container is analyzed using isochoric conditions. This helps understand how sound waves propagate and interact with their surroundings.
  • Isochoric conditions are employed in some chemical reactions, particularly those involving gases. Researchers may use sealed containers to perform chemical reactions at a constant volume, controlling reactant concentrations and studying reaction kinetics.
  • In materials science, isochoric conditions are useful for studying the response of materials to pressure without volume changes. This is important for understanding material behavior under high-pressure conditions.
  • Isochoric processes play a role in thermodynamic studies, particularly when investigating phase transitions, equations of state, and specific heat capacities under constant volume conditions.

Isobaric Processes

  • Isobaric processes are common in heat exchangers, where fluids at a constant pressure are used to transfer heat efficiently. This is essential in applications like air conditioning and refrigeration.
  • In steam power plants, an isobaric process is employed during the phase where high-pressure steam is used to turn turbines, generating electricity.
  • Many chemical processes occur under isobaric conditions, such as distillation, where different components of a mixture are separated based on their boiling points at constant pressure.
  • Isobaric conditions are used in canning and sterilization processes to maintain constant pressure, ensuring the preservation and safety of food products.
  • Isobaric chambers are used in the aerospace industry to simulate conditions at high altitudes and low atmospheric pressure, allowing testing and validation of aircraft and spacecraft components.
  • Environmental chambers that maintain constant pressure conditions are utilized for testing the behavior of materials, equipment, and electronics under varying environmental conditions, including pressure changes.
  • Analytical techniques such as high-pressure liquid chromatography (HPLC) and high-pressure gas chromatography (HPGC) rely on isobaric conditions to separate and analyze complex mixtures of compounds.
  • Pharmaceutical processes often require precise pressure control. Isobaric conditions are used in drug formulation, chemical synthesis, and quality control.
  • Isobaric conditions are encountered in oil and gas reservoirs, where the pressure of hydrocarbons is controlled and monitored.
  • In metallurgical processes like heat treatment, controlling pressure is essential for achieving desired material properties.

Key Takeaways

isochoric vs isobaric process

Concepts Berg

What is an isochoric process, and when is it encountered?

An isochoric process, also known as a constant volume process, maintains a fixed volume (∆V = 0) while allowing pressure and temperature changes. It is commonly encountered in calorimetry experiments, such as bomb calorimeters, and the study of reactions in sealed containers.

What is an isobaric process, and where do we find it in real-life applications?

An isobaric process maintains constant pressure while volume and temperature can vary. Isobaric processes are prevalent in applications like heat exchangers, chemical reactions conducted under constant pressure, and power generation, as seen in steam power plants.

What’s the primary difference between isochoric and isobaric processes?

The fundamental distinction is that in an isochoric process, the volume remains constant, while in an isobaric process, the pressure remains constant.

Can work be done during an isochoric process?

No, mechanical work is not done in an isochoric process, as the volume does not change (∆V = 0). Consequently, the work done in an isochoric process is zero.

How is work calculated in an isobaric process?

Work in an isobaric process is calculated using the formula W = P∆V, where P is the constant pressure and ∆V represents the change in volume. Work may be done by or on the system during isobaric processes.

Are isochoric processes limited to gases only?

No, isochoric processes are not limited to gases. They are relevant for any substance where the volume remains constant, including liquids and solids, in addition to gases.

Can you provide an example of an isochoric process in daily life?

When you boil water in a closed, rigid container like a pressure cooker, it operates as an isochoric process, maintaining constant volume as the water changes phase and temperature.

What’s the significance of maintaining constant pressure in isobaric processes?

Constant pressure in isobaric processes allows for consistent conditions for chemical reactions and energy transfers. It’s vital in applications like distillation, where specific boiling points are required.

How do isochoric and isobaric processes impact thermodynamic experiments?

Isochoric processes enable the measurement of heat effects and energy changes under constant volume, vital in calorimetry. Isobaric processes are valuable for studying chemical reactions under constant pressure and for power generation.

Can these processes occur simultaneously in a single system?

Yes, in some systems, processes can involve both isochoric and isobaric stages. For instance, in a combustion engine, there’s an isochoric ignition phase followed by an isobaric expansion phase to generate power.