In isovolumetric processes, the volume remains constant and therefore no work is performed. The heat exchanged with the medium is equal to the change in the system's internal energy (see graph above).
According to the First Law of Thermodynamics, in any thermodynamic process the amount of heat Q received by a system is equal to the work done by it plus the variation of its internal energy. Thus, the equation that represents the first law follows below:
Q=τ+∆U
As stated in the first paragraph, where it says that there is no work, we have to τ=0. Thus, the heat exchanged with the medium is equal to the increase in the system's internal energy. Thus, we have:
Q=∆U
When heat is supplied to the system, that is, when Q is positive, the internal energy will increase; and when the system loses heat, that is, when Q is negative, the internal energy will decrease. Constant volume processes occur when the container containing the material is rigid (eg a gas cylinder).
When receiving heat, the system tends to expand but is impeded by the vessel walls, so the pressure and temperature of the system increase.
By Domitiano Marques
Graduated in Physics
Source: Brazil School - https://brasilescola.uol.com.br/fisica/primeira-lei-para-processos-isovolumetricos.htm
