Effect of Pressure Change

The final stress we will consider is that caused by either an increase or a decrease in the pressure within the reaction chamber. This pressure stress is akin to the pressure changes discussed for systems of gases in Chapter 9. In fact, within reasonable limits, the only time a pressure change is usually a stress on an equilibrium system is when one or more gases are involved in the equilibrium. If no gases are involved, then the equilibrium does not shift in either direction. 

Pressure stresses can be thought of as either pushing down or pulling up on the piston in the piston-cylinder arrangement in Chapter 9 when the equilibrium reaction is occurring within a volume enclosed by the piston and cylinder. Pushing down on the piston means a pressure increase in the system, while pulling up on the piston means a pressure decrease in the system. 

All the reactants and products in this reaction are gases. There are four moles of gas on the left and two moles of gas on the right. If the pressure is increased, the equilibrium would shift toward the side where there is less gas. This relieves the stress by decreasing the pressure due to less gas being present. This means that the equilibrium will be a shift to the right in this case. 

In each case, the system returns to the equilibrium state of Equation 11.29. 

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Operating the column under atmospheric pressure thereby eliminating the need for the vacuum pump. Here a simulation study is needed to examine the effect of pressure change. 

The equilibrium constant Ka is independent of pressure for those cases where the standard states are taken as the pure components at 1 atm. This case is the one used as the basis for deriving equation 2.6.9. Tjie effect of pressure changes then appears in the terms KfjP and ps + t+ b c . The influence of pressure on KfjP is quite small. However, for cases where there is no change in the total number of gaseous moles during the reaction, this is the only term by which pressure changes affect the equilibrium yield. For these... 

The effects of pressure changes in various sections of the column on the physical properties of the system being distilled are negligible. 

We should note that in most cases in environmental organic chemistry, we can neglect the effect of pressure changes on equilibrium partitioning. Exceptions might... 

These relationships are represented in an exaggerated manner in fig. 2. The lines AO, BC and OD represent the vapour pressures of sulphur I., sulphur II. and molten sulphur, respectively OE and CF show the effect of pressure change on the melting-points of the two crystalline forms, whilst the effect of pressure on the transition temperature is indicated by BF. 

In applying Le Chatelier s principle to a heterogeneous equilibrium, the effect of pressure changes on solids and liquids can be ignored because the volume (and concentration) of a solid or a liquid is nearly independent of pressure. Consider, for example, the high-temperature reaction of carbon with steam, the first step in converting coal to gaseous fuels ... 

The effect of pressure change is a complicated issue. If we have a reaction like a dissociation reaction, for example (Frame 45, reaction (45.24)) ... 

Notice that the pressure change term in the first step (V AP = -0.0782 kJ/mol) accounts for less than 0.1% of the overall process enthalpy change. We will generally neglect the effects of pressure changes on A/ unless AP is on the order of 50 atm or more. 

The Effects of Pressure Change on the Rate of a Gaseous Reaction... 

EFFECTS OF PRESSURE CHANGES ON THE EQUILIBRIUM STATE IN GASEOUS REACTIONS... 

Table 4A2.1. Parameters for calculating the effect of pressure change on carbonate buffer system reactions and values of equilibrium constants at P = 0 and 300 bar ...

Figure 5. Measured (solid lines) effect of pressure changes on WGS rate compared to effect predicted by oxygen transfer (regenerative) mechanism (dashed lines). (AP = 0 corresponds to all P - = 10 kPa). Reproduced with permission from Ref. 37. Copyright 1982, AIChE.

The Effect of Pressure Changes on the Electromotive Force of Galvanic Cells. If we apply equation (23) to the reacting substances and the products of a chemical reaction and subtract one from the other we obtain... 

The effect of pressure changes on the DTA curve has been studied by numerous investigators. Increasing the pressure in the system, even with an inert gas, increases the transition temperatures, A7 in, and 7. At low pressures < i Torr, the product gases are removed rapidly hence the... 

Kamphausen et al. (21) determined the effect of pressure changes from ambient atmospheric to 2 kbar on the DSC curves of heneicosane, n-C,H44.. 

The effect of C02 pressure on the shape of the DTA curve of dolomite has been discussed by Bandi and Krapf (137). At pressures of less than 200Torr, a one-step decomposition to CaO and MgO was observed at higher pressures of C02, a two-step process was found. It was concluded that the reaction mechanism was different at the lower pressures from that at higher pressures. Criado (138) has derived several equations proving that this is not the case but is merely the effect of pressure change on the fraction of sample reacted, a. He showed that between 500 and 1000°C the decomposition of CaC03 can be fitted closely by the equation... 

A 10 m long vertical standpipe of inside diameter 0.1 m transports solids at a flux of 100 kg/m s from an upper vessel which is held at a pressure 1.0 bar to a lower vessel held at 1.5 bar. The particle density of the solids is 2500 kg/m and the surface-volume mean particle size is 250 gm. Assuming that the voidage is constant along the standpipe and equal to 0.50, and that the effect of pressure change may be ignored, determine the direction and flow rate of gas passing between the vessels. (Properties of gas in the system density, 1 kg/m viscosity, 2 x 10 Pas.)... 

The anti-smge vessel consists of a self-contained protective device, which safeguards against both over- and under-pressmes. The elastic membrane inside the tank, which isolates the liquid from a volume of air, moves under the effect of pressure changes, converting the pressure variations in the hqnid into compressed air. At the same time, the membrane should be elastic to respond to pressure variations, and quickly contribute to the dissipation of pressure fluctuations. 

Effect of Pressure Changes on Liquid-Phase Activity Coefficients... 

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