Isochoric and Isobaric Processes

In an isochoric process, volume remains constant, so no work is done by the system. According to the first law of thermodynamics, all heat added to the system is converted entirely into internal energy change. For example, heating water in a sealed container increases only its internal energy without performing any work on surroundings.

An isobaric process occurs at constant pressure, while an isochoric process occurs at constant volume. In isobaric processes, the system performs work as volume changes. Heat added is split between increasing internal energy and performing work. In isochoric processes, no work occurs and all heat increases internal energy only.

The pV diagram for an isochoric process is represented by a vertical line parallel to the pressure axis. This vertical line indicates that volume remains constant while pressure may change. The diagram visually demonstrates that no volume change occurs during the process, distinguishing it from other thermodynamic processes.

In an isobaric process, work done equals the product of constant pressure and the change in volume. If volume expands, the system does positive work on surroundings. If volume contracts, work is done on the system and is negative. This work calculation is essential for understanding energy distribution in constant-pressure processes.

Evaporation occurring inside a sealed ecosystem is an isochoric process. Since water vapor cannot escape the sealed container, the volume remains constant. The heat added to the system increases only the internal energy of the water and air mixture without performing external work.

Boiling water in an open container is an isobaric process because atmospheric pressure remains constant throughout. As water evaporates and converts to steam, the volume increases while pressure stays constant. The heat supplied performs work against atmospheric pressure while also increasing the internal energy of the system.

Heat added in an isochoric process equals the product of mass, specific heat, and temperature change. For example, heating 1000 g of water from 40°C to 70°C at constant volume involves a 30 K temperature change. Using water's specific heat of 4184 J/kg·K, the heat added is approximately 125.52 kJ, all converting to internal energy.