Слайд 2 An isobaric or isobar process is a thermodynamic process occurring
in the system at constant pressure and mass of gas.
According
to the Gay-Lussac law, in an ideal gas with an isobaric process, the ratio of volume to temperature is constant: V/T=const
If we use the Clapeyron – Mendeleev equation, then the work performed by a gas during gas expansion
The amount of heat received or given off by the gas is characterized by the change in enthalpy
Слайд 3Isobaric gas expansion graph
Слайд 4Heat capacity
The molar heat capacity at constant pressure is denoted
as Cp. In ideal gas, it is related to heat
capacity at constant volume by the Mayer ratio.
Molecular-kinetic theory allows to calculate the approximate values of the molar heat capacity for various gases through the value of the universal gas constant R:
-for monatomic gases
-for diatomic gases
-for polyatomic gases
Heat capacity can also be determined from the Mayer equation if the adiabatic index is known, which can be measured experimentally (for example, by measuring the speed of sound in a gas or using the Clement-Desorption method).
Слайд 6Isobaric processes in different coordinate systems
Слайд 7Liquefied gases are stored in vessels communicating with the atmosphere.
Is it possible to allow evaporation of liquid nitrogen with
a volume of 0.5 l and a density of 0.81 g / cm3 in a closed vessel with a volume of 10 l when it is heated to a temperature of 20 C if the vessel walls withstand a pressure of 20 atm?
Decision. When the temperature rises, the liquid nitrogen will become gaseous. We take it at a temperature of 20C for an ideal gas and apply the Clapeyron – Mendeleev equation to solve:
Слайд 9Answer: evaporation of liquid nitrogen of a given mass in
a closed vessel of the specified volume cannot be allowed,
since at 20 C the pressure will exceed the allowable one. Therefore, liquefied gases are stored in open vessels.
