# What is the Difference Between Isobaric and Isochoric Process

The main difference between isobaric and isochoric processes is that isobaric processes maintain a constant pressure, while isochoric processes maintain a constant volume.

Isobaric and isochoric processes are fundamental concepts in thermodynamics that describe how a system undergoes changes in its state variables, such as pressure, volume, and temperature.

### Key Areas Covered

1. What is Isobaric Process
– Definition, Work Done, Heat Transfer
2. What is Isochoric Process
– Definition, Work Done, Heat Transfer
3. Similarities Between Isobaric and Isochoric Process
– Outline of Common Features
4. Difference Between Isobaric and Isochoric Process
– Comparison of Key Differences

### Key Terms

Constant-Volume Process, Isobaric Process, Isochoric Process

## What is Isobaric Process

An isobaric process refers to a thermodynamic transformation that occurs at constant pressure, enabling us to analyze the changes in other properties, such as volume and temperature, while the pressure remains unchanged.

Since the pressure of a system remains constant, any changes occurring within the system involve adjustments in other properties. These changes are governed by the principles of the ideal gas law and can be mathematically expressed as:

P * ΔV = n * R * ΔT

where P is the constant pressure, ΔV represents the change in volume, n is the number of moles of the gas, R is the gas constant, and ΔT stands for the change in temperature.

Figure: Isobaric Process

Let’s consider a practical example to illustrate the isobaric process better. Imagine a container filled with a certain amount of gas fitted with a movable piston. If the gas is heated while the piston is free to move, the temperature and volume of the gas will increase. However, the pressure inside the container remains constant, as it is allowed to escape and equalize with the surroundings. The change in volume and temperature results from the added thermal energy, but the pressure remains unchanged during the process.

Isobaric processes are crucial in various applications. In internal combustion engines, they enable efficient conversion of fuel energy into mechanical work. Meteorologists use them to predict weather patterns by studying constant atmospheric pressure areas. Air conditioning and refrigeration rely on isobaric stages for heat transfer and temperature control. Industries manipulate gases in chemical reactions and storage using these processes for safety and efficiency. Aeronautical and aerospace engineering apply isobaric understanding in designing engines and propulsion systems for aircraft and rockets.

## What is Isochoric Process

Also known as the constant-volume process, the isochoric process occurs when a system undergoes a transformation while keeping its volume constant. Since the volume of the system remains unchanged throughout the transformation, any change in the system’s internal energy is solely attributed to heat transfer, as no work is done during the process. Mathematically, the isochoric process can be described as:

ΔV = 0

where ΔV represents the change in volume during the process.

Since the volume remains constant, any increase in heat supplied to the system results in an increase in temperature without any change in volume. According to the ideal gas law (PV = nRT), if the volume is held constant (V is constant), the pressure (P) and temperature (T) are directly proportional. As the temperature rises, the pressure of the confined gas also increases. As mentioned earlier, during an isochoric process, no work is done by the system or on the system. This is because work (W) is defined as the product of force (F) and displacement (d), W = F × d. In this case, d = 0, resulting in W = 0.

The internal energy change (ΔU) of the system in an isochoric process is equivalent to the heat (Q) added to or removed from the system. Mathematically, this relationship can be expressed as ΔU = Q.

Figure 2: Isochoric Process

### Uses of Isochoric Processes

Isochoric processes are often employed in calorimetry experiments to measure the heat capacity of substances. A constant-volume calorimeter is used to conduct such experiments. By keeping the volume constant, the heat transferred can be directly related to the temperature change of the system, providing valuable information about the specific heat capacity of materials.

The concept of isochoric processes plays a crucial role in internal combustion engines. During the combustion stroke of an engine, the fuel-air mixture ignites, causing a rapid increase in temperature and pressure.

## Similarities Between Isobaric and Isochoric Process

• Isobaric and isochoric processes occur in thermodynamic equilibrium.
• Both processes involve heat transfer between the system and its surroundings.
• The first law of thermodynamics, also known as the law of energy conservation, applies to both isobaric and isochoric processes.

## Difference Between Isobaric and Isochoric Process

### Definition

An isobaric process is a thermodynamic transformation where a system undergoes a change while maintaining constant pressure, often leading to work being done on or by the system. An isochoric process occurs when a system undergoes a change while keeping its volume constant, typically resulting in changes in temperature and pressure.

### Nature

In an isobaric process, the pressure of the system remains constant throughout the transformation. While the volume and temperature can change, the pressure is fixed. In an isochoric process, the volume of the system remains constant during the transformation. The pressure and temperature can change, but the volume remains unchanged.

### Work Done

Work is done in an isobaric process as the volume changes against a constant pressure. The work done is given by the formula W = PΔV, where P is the constant pressure, and ΔV is the change in volume. However, no work is done in an isochoric process as the volume remains constant throughout the transformation (ΔV = 0). Consequently, the work done is zero (W = 0).

### Heat Transfer

In an isobaric process, heat transfer can lead to changes in both temperature and volume. The heat added to the system (Q) results in an increase in the system’s internal energy (ΔU = Q – PΔV) and may cause the volume to expand or contract. In an isochoric process, heat transfer only affects the system’s internal energy (ΔU = Q) since the volume remains constant (ΔV = 0). The heat added or removed directly contributes to changing the system’s temperature.

## Conclusion

Isobaric and isochoric processes are fundamental concepts in thermodynamics. The main difference between isobaric and isochoric process is that isobaric processes maintain a constant pressure, while isochoric processes maintain a constant volume.

##### Reference:

1. “Isobaric Process – Definition, Formula, Examples, FAQs.” Byju’s.
2. “Isochoric Process – An Overview.” Science Direct.

##### Image Courtesy:

1. “Isobaric process plain” By IkamusumeFan – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “Isochoric process SVG” By IkamusumeFan – Own work (CC BY-SA 3.0) via Commons Wikimedia

### About the Author: Hasini A

Hasini is a graduate of Applied Science with a strong background in forestry, environmental science, chemistry, and management science. She is an amateur photographer with a keen interest in exploring the wonders of nature and science.