 Let us consider a system with an ideal gas in it. The state of the gas, or more precisely, its temperature, t, its pressure, pi, and its volume, v, are described by the ideal gas equation. Pi is equal to n times r times t times 1 divided by v. n is the amount of substance and indirectly describes the number of gas particles. And r is the gas constant. We refer to temperature, pressure, and volume as properties. They describe the macroscopic state of the gas. If we heat the gas and thus increase its temperature, t, we are talking about a thermodynamic process. We could also compress the gas, thereby increasing the pressure and reducing the volume. This would also be a thermodynamic process. The thermodynamic process can be isobaric, isothermal, isochoric, or adiabatic. In the case of an isobaric process, the pressure of the gas remains constant. This means that pi, n, and r are pure constants in the gas law. And the volume v is proportional to the temperature, t. The pressure volume diagram results in a horizontal straight line for an isobaric gas. This means that a change in volume does not lead to a change in gas pressure. During an isochoric process, the volume v of the gas remains constant. Then v, n, and r are constants in the gas law. And the pressure pi is proportional to the temperature, t. The pressure volume diagram shows a vertical straight line for an isochoric gas. The change in gas pressure does not lead to a change in volume. During an isothermal process, the temperature, t of the gas remains constant. This means that the pressure pi is proportional to the inverse volume, 1 over v. The pressure volume diagram shows a decreasing curve for an isothermally behaving gas. Increasing the volume of the gas leads to a reduction in the gas pressure. During an adiabatic process, no thermal energy is transported out and into the system. During this process, the temperature, t, volume v, and pressure pi of the gas can change simultaneously. The pressure volume diagram shows a power law behavior for an adiabatically behaving gas. The exponent gamma is referred to as the adiabatic exponent.