Transformation of energy

Thermal energy and combustion.
Effects of thermodynamics


Isobaric Process

Isobaric Process

In thermodynamics, an isobaric process is a change in the state of a certain amount of matter in which the pressure does not change, but one or more of its state variables. An example of this is air in a cylinder with a freely movable piston to which heat is supplied. Due to the increase in temperature, the volume will increase, but the pressure will remain constant.

The isobaric process is governed by Charles's law. The Frenchman Jacques A. Charles (1742-1822) was the first to make measurements about gases that expand when their temperature increases.

Examples of isobaric processes

To better understand this thermodynamic process, it will help us to see a couple of examples.

An everyday example of an isobaric process occurs when boiling water in an open container. By supplying heat energy to water, it rises in temperature and becomes steam. The steam that is obtained has a higher temperature and occupies a greater volume, however, the pressure remains constant. From the beginning, the pressure is equal to the atmospheric pressure.

Another example is the volume variation that a balloon experiences as the sun's rays indicate on it. At the beginning of the morning, it has some pressure, volume and temperature, as the air inside increases, the pressure increases, but this does not change due to the increase in its volume.

Unlike the previous example, heating water in a circuit of a solar thermal installation is not an isobaric process. In this case the water circulates through a closed circuit, so that it can not increase the volume. When the water begins to receive the heat energy that comes from the solar radiation in a solar panel, it increases its temperature. It increases the temperature, but can not increase the volume, so that it can only increase the pressure to maintain thermodynamic equilibrium.


1-2 = P ( 2 - 1 )
1-2 = R ( 2 - 1 )
1-2 = p ( 2 - 1 )
1-2 = ( k / ( k -1)) P ( 2 - 1 )



  • W 1-2 the work done by the change of state
  • Q 1-2 the amount of heat supplied or removed
  • P the pressure
  • V the volume
  • T the absolute temperature
  • n the amount of dust (usually expressed in moles)
  • m the mass of the substance
  • c p the specific heat of the substance at constant pressure
  • k is a ratio equal to the quotient of the specific heat at constant pressure and constant volume, respectively

Published: April 24, 2018
Last review: April 24, 2018