# Difference Between Isothermal and Adiabatic Process

## Main Difference – Isothermal vs Adiabatic Process

Thermodynamics uses the concepts isothermal process and adiabatic process to explain the behavior of a thermodynamic system and its relation to the temperature changes. Isothermal process is a process that happens under constant temperature, but other parameters regarding the system can be changed accordingly. Adiabatic process describes a process where no heat transfer occurs between a system and its surrounding. Here, the temperature of the system should be changed in order to avoid any heat transfer. This indicates that the main difference between isothermal and adiabatic process is that isothermal process occurs under constant temperature whereas adiabatic process occurs under varying temperature.

### Key Areas Covered

1. What is an Isothermal Process
– Definition, Characteristic Features
2. What is an Adiabatic Process
– Definition, Characteristic Features
3. What is the Difference Between Isothermal and Adiabatic Process
– Comparison of Key Differences

Key Terms: Adiabatic Process, Isothermal Process, Surrounding, System, Thermodynamic System

## What is an Isothermal Process

An isothermal process is a thermodynamic process that occurs under a constant temperature. This means an isothermal process occurs in a system where the temperature is constant. In order to keep the temperature of the system constant, heat should be transferred out of the system or into the system.

Apart from that, some other factors of the system also change during the progression of an isothermal process such as internal energy. To maintain the temperature of the system, it can be kept in a heat bath. Then, by regulating the temperature of the heat bath, we can control the temperature of the system to an appropriate level.

Figure 1: A curve for an isothermal process regarding an ideal gas.

Examples for isothermal processes include phase change of matter, melting of matter, evaporation, etc. One industrial use of isothermal process is carnot heat engine. In order to maintain the temperature of the system, work should either be done on the system or be done by the system on surrounding; doing work on the gas increases the internal energy, and the temperature is increased. But if the temperature is higher than the required level, then work is done by the system on the surrounding. Then the temperature of the system is decreased since the energy is released to the surroundings as heat.

## What is an Adiabatic Process

Adiabatic process is a thermodynamic process that occurs without any heat transfer between a system and its surrounding. Here, either heat or matter is not transferred into or out of the system. Therefore, in adiabatic process, the only way energy transfers between a system and its surrounding is as work.

Figure 2: An Adiabatic Process

An adiabatic process can be maintained by quickly doing the process. For example, if we quickly compress a gas in a cylinder, there’s not enough time for the system to transfer heat energy to the environment. In adiabatic processes, the work done by the system changes the internal energy of the system.

## Difference Between Isothermal and Adiabatic Process

### Definition

Isothermal Process: An isothermal process is a thermodynamic process that occurs under a constant temperature.

Adiabatic Process: Adiabatic process is a thermodynamic process that occurs without any heat transfer between a system and its surrounding.

### Heat Transfer

Isothermal Process: Heat transfer can be observed in isothermal processes.

Adiabatic Process: There is no heat transfer in adiabatic processes.

### Temperature

Isothermal Process: The temperature is constant for isothermal processes.

Adiabatic Process: The temperature can be changed in adiabatic processes.

### Work

Isothermal Process: In isothermal processes, the work done is due to the change in the net heat content of the system.

Adiabatic Process: In adiabatic processes, the work done is due to the change in its internal energy.

### Conclusion

Isothermal and adiabatic processes are thermodynamic processes. These processes describe the relationship between internal energy of a system and its changes. The main difference between isothermal and adiabatic process is that isothermal process occurs under constant temperature whereas adiabatic process occurs under varying temperature.

##### References:

1. “Isothermal process” By Yuta Aoki – Original (CC BY-SA 3.0) via Commons Wikimedia
2. “Adiabatic process” By Yuta Aoki – Original (CC BY-SA 3.0) via Commons Wikimedia

##### References:

1. Jones, Andrew Zimmerman. “The Definition of the Isothermal Process.” ThoughtCo, Available here.
2. “Isothermal process.” Wikipedia, Wikimedia Foundation, 12 Oct. 2017, Available here.
3. “Adiabatic Process.” Hyperphysics. Available here.