Final control questions on the subject “heat engineering” The purpose and function of the subject. Working parameter. Status parameters. Base words and phrases

14. Isothermal process. 
 
Base words and phrases: temperature, diagrams, internal energy, work, amount of heat, 
enthalpy, entropy 
An isothermal process is a thermodynamic process during which the temperature of a system 
remains constant, and so the internal energy is held constant. In other words, the system is 
held at a constant temperature throughout the process. An isothermal process can occur rapidly 
if thermal energy is transferred to or from the system.
Here are the base words and phrases related to an isothermal process:
- Temperature: During an isothermal process, the temperature of the system remains constant. This 
means that the pressure and volume of the system are inversely proportional, according to the 
ideal gas law PV = nRT.
- Diagrams: Isothermal processes are represented on thermodynamic diagrams, such as the 
pressure-volume (PV) or temperature-entropy (TS) diagrams. On a PV diagram, an isothermal 
process is represented by a curved line linking the initial and final states of a system. 
- Internal energy: The internal energy of the system remains constant throughout an isothermal 
process since there is no change in temperature. Instead, the heat entering the system is 
converted into work, or vice versa. 
- Work: During an isothermal process, the total work done by or on the system can be calculated 
through the area enclosed by the curved line on a PV diagram. In this case, the work is the 
integral of the pressure over the change in volume(via integration). 
- Amount of heat: The amount of heat transferred during an isothermal process depends on the 
work done by or on the system. This is due to the fact that the amount of heat added or removed 
from the system is equal to the work done against or by osmotic force. 
- Enthalpy: The enthalpy change in an isothermal process is equal to the work done on the system, 
since the internal energy of the system remains constant.

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- Entropy: Unlike isochoric and isobaric processes, the entropy of the system may change during 
an isothermal process as entropy may arise from heat transfer over time if it takes place in an 
open system. 
In summary, an isothermal process occurs at a constant temperature with the changes in volume, 
pressure, internal energy, work, amount of heat, enthalpy, and entropy. The internal energy of 
the system remains constant throughout, meaning that the work done by or on the system can 
be used to calculate the amount of heat added or removed from the system. The enthalpy 
change of the system is equal to the work done on the system, while the entropy of the system 
may change due to heat transfer over time if it takes place in an open system. 
15. Adiabatic process.