Constant pressure, gas

This equation is usually valid for liquid-phase reactions and for gas reactions where the sum of the stoichiometric numbers equals zero, but it is invalid for constant pressure gas-phase reactions with mole changes. 

Volume variations with conversion are large for constant-pressure gas-phase reactions with change in mole number. Here, as a rule, operation at constant volume poses no difficulties. Liquid-phase reactions may also entail volume contraction or expansion. However, these are not related to changes in mole number and can be predicted only if information on partial molar volumes is at hand. Because liquids are essentially incompressible, even at elevated temperature, it is unsafe to conduct liquid-phase reactions without a gas cap in a closed reactor. Some variation of liquid-phase volume with conversion therefore is apt to occur. Fortunately, the variation at constant temperature is usually so small that it can be neglected in the evaluation or accounted for by a minor correction. 

If in the rare case that the reactor is accomplishing a constant pressure gas-phase reaction at nonisothermal conditions ... 

For constant-temperature and constant-pressure gas-phase reactions, the concentration is expressed as a function of conversion ... 

Figure 11 Lavoisier s constant pressure gas pump and reaction vessels.

Ideal Gas Scale. It is found experimentally that the temperature measured in the constant-pressure gas thermometer, with V as the thermometric property, has a limiting value as the pressure tends to zero ... 

Calibrated gasometers or gas burettes are used. A constant-pressure gas burette was described by Schenk [Z. anorg. allg. Chem. 233, 393 (1937)]. Otherwise, wet test meters—commercially available in precision t3q)es—are used. They are especially useful in calibration of flow meters. 

Energetics. Regardless of the gas phase combustion kinetics and thermochemistry, burning will only be possible if the energy balance is favorable. The first law of thermodynamics for a constant pressure gas phase process in which all of the work is pressure-volume (P-V) work states that the internal energy change dLT is related to the change in heat content dQ ... 

B. at constant pressure, gas volume is direcdy proportional to absolute temperature. 

ILLUSTRATIVE EXAMPLE 5.14 Consider the irreversible, elementary, isothermal constant pressure gas phase reaction below for C estions (1-7) ... 

Temperature-programmed reduction (TPR) measurement was carried out by a volumetric method with a constant pressure gas circulation system of ca. 200 ml. Liquid nitrogen traps were placed before and after a quartz measuring tube to remove the water formed. After evacuation of sample at 573 K for 30 min, the temperature of the sample was decreased to room temperature, and a constant pressure of hydrogen was admitted to the system. Then the temperature was increased at a rate of 5.3 K/min. 

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