Short Answer:

An isochoric process is a thermodynamic process in which the volume of the system remains constant. In this process, even if heat is added or removed, the volume does not change at all. As a result, no mechanical work is done by the system since work requires a change in volume.

An example of an isochoric process is heating a gas in a sealed, rigid container. Since the container doesn’t allow the gas to expand, all the heat added increases the internal energy and temperature of the gas, not its volume. Isochoric processes are important in analyzing heat changes without volume change.

Detailed Explanation:

Isochoric process

In thermodynamics, an isochoric process (also known as an isometric or isovolumetric process) is a process that occurs at a constant volume. The term “isochoric” comes from the Greek words “iso” meaning same and “chore” meaning space or volume, which together mean same volume. In this process, volume stays fixed, and only heat and internal energy change.

Since volume is constant, there is no movement of the system’s boundaries, and therefore no work is done by or on the system. This condition makes the isochoric process ideal for studying how heat affects internal energy and temperature alone.

Key Features of Isochoric Process

Constant volume (V = constant):
There is no change in the system’s size or volume during the process.
No work done (W = 0):
In thermodynamics, work done (W) = P × ΔV. Since ΔV = 0, then W = 0.
Change in internal energy (ΔU ≠ 0):
All the heat added or removed from the system goes into changing its internal energy.
Change in pressure and temperature:
Even though volume is constant, both pressure and temperature can increase or decrease depending on heat transfer.
Useful for studying energy and heat change when volume cannot expand.

Thermodynamic Equation for Isochoric Process

According to the First Law of Thermodynamics:

ΔU = Q – W

But for an isochoric process, W = 0, so:

ΔU = Q

This means that all the heat added to the system directly increases the internal energy of the system. For an ideal gas, this results in a temperature increase. If heat is removed, internal energy and temperature decrease.

Example of Isochoric Process

Heating a gas in a sealed rigid container:
Suppose you take a steel cylinder filled with gas and tightly close it. When you heat this cylinder, the gas cannot expand (because the volume is fixed), so it cannot do any work. The only effect of the heat will be to increase the gas’s internal energy and temperature. This is a clear example of an isochoric process.

Other Examples:

Fuel combustion in a closed combustion chamber before the piston moves (idealized in Otto cycle).
Heating liquid in a pressure cooker before steam escapes.

Importance in Thermodynamic Cycles

Isochoric processes are a part of many ideal thermodynamic cycles like:

Otto cycle (used in petrol engines): Heat addition is considered at constant volume.
Stirling cycle: Includes isochoric heating and cooling steps.
Air standard cycles: Many cycles assume isochoric heat addition or rejection for simplicity.

These processes help simplify calculations and understand how internal energy changes affect engine performance.

Pressure-Temperature Relationship

In an isochoric process with an ideal gas, pressure and temperature are directly related:

P / T = constant

This means that if temperature increases, pressure also increases, and vice versa. This is why sealed containers can explode when heated — the volume cannot increase, so pressure rises dangerously.

Real-Life Use and Caution

In real systems, isochoric conditions happen when the container or chamber is completely rigid. Engineers must be careful while heating such systems because the pressure can increase rapidly, leading to damage or safety risks.

Conclusion

An isochoric process is a thermodynamic process where volume remains constant and no work is done. Any heat added or removed goes directly into changing the internal energy and temperature of the system. This process is very important in engine cycles, heating systems, and in the design of closed containers under pressure. It gives engineers a clear understanding of how energy behaves when the system cannot expand or contract.