P V work

The p V work temi is not nomially measured. It can be eliminated by suspending the calorimeter in an evacuated space (p = 0) or by holding the volume of tire calorimeter constant (dF= 0) to give... 

All applications are for closed systems with constant mass. If a process is reversible and only p-V work is done, the first law and differentials can be expressed as follows. 

If a change from state A to state B occurs in a system at constant pressure (isobaric) so that only p V work is done, then w = pA V and... 

Protein biomolecules consisting of polypeptide chain with large molecular mass Protostar early stage in the formation of a star when gases and dust start to contract due to gravitational forces P-V Work work associated with the expansion or compression of a gas Pyrethroids synthetic forms of pyrethrins, insecticides based on extracts from chrysanthemums... 

The pressure-volume (P-fO work associated with an initial intrusion-extrusion cycle can be calculated from the areas above curves A and C to the maximum intruded volume, indicated by the horizontal dotted line in Fig. 12.1. (The work associated with any graphical area can be calculated with reference to equations (11.8) and (11.9).) This P-V work, I dlTj, can be expressed as... 

Even in the absence of mercury entrapment, second or subsequent intrusion-extrusion cycles, curves B and C of Fig. 12.1, continue to show hysteresis with the P-V work, dW2, through a cycle given by... 

As illustrated in Fig. 12.1 the P-V work through a second cycle is always less than that through a first cycle since the areas between curves B and C is less than that between A and C. Then,... 

The total area above the first intrusion curve, A in Fig. 12.1, to the maximum intruded volume indicated by the horizontal dotted line, corresponds to the P-V work of intrusion, IFj. This work term consists of three parts, the first of which is the work of entrapment, W, corresponding to the area between curves A and B. The second contribution to IF. is the work, fV g, associated with the contact angle change from 0, to 0 ... 

It is evident that the thermodynamic processes associated with mercury porosimetry are far more complex than just the consideration of P-V work. 

The P-V work differences between intrusion and extrusion, corresponding to the area between curves. A and C of Fig. 12.1 can be expressed as... 

The physical meaning of the Helmholtz free energy is similar to that of the Gibbs energy, both being criteria to define - equilibrium. The equilibrium criterion in a closed system, which is only capable of doing P-V work and held at constant temperature and volume, is the minimum of Helmholtz energy. See also Helmholtz. 

Several important points must be made in connection with Table 1.16.1 (i) There is a common misconception to the effect that the performance of work is exclusively associated with a change in the internal energy of the system. Clearly, in general this is not the case. If, for example, a process is carried out at constant T and P, then the performance of work other than P-V work is associated with a change of the Gibbs free energy. (ii) For each of the five conditions under which processes are shown to occur in Table 1.16.1, there is a special function of state best suited to describe the process furthermore, under the various indicated conditions the inexact... 

Expand on the analysis of this section by examining cases where work other than mechanical (P-V) work is involved. 

We can express ASsurr in terms of the change in enthalpy (AH) for a process occurring at constant pressure (where only P V work is allowed), since under these conditions... 

Consider an ideal gas confined to a cylinder with a movable piston, as shown in Fig. 10.18. Initially, the pressure of the gas (Pgas) equals the external pressure (Pext) and the piston is stationary. If Pext is decreased, the gas will expand by doing P V work. What will happen to the temperature of the gas (Remember that q = 0.) Because the expanding gas does work on the surroundings,... 

The compressed gas temperature calculated by (6.16) does not represent an appropriate reference temperature when the fuel + air mixture is so reactive that exothermic oxidation begins during the compression stroke. The pressure reached at the end of compression does not then arise solely form p-V work, and application of a thermodynamic relationship (6.16) based on the measured pressure is not valid. The ideal gas equation may be applied to the system in these circumstances, the compressibility factor... 

How must the derivation of the Gibbs phase rule be modified if work other than mechanical P-V work is performed on or by the system (Hint classify these degrees of freedom with P and V and proceed with an expanded derivation.)... 

The quantity which is generally more accessible experimentally is the enthalpy. The enthalpy of dissociation at a given temperature differs from the energy of dissociation by P V work 2.5 kJ mol" 600 cal mol at room temperature. Some examples of the various quantities for Hj are ... 

A gas expands and does P-V work on the surroundings equal to 279 J. At the same time, it absorbs 216 J of heat from the surroundings. What is the change in energy of the system ... 

The sign convention for electrical work is the same as that for P-V work, discussed in Section 6.7. 

We have thus far restricted our discussion to plane interfaces. However, because of the existence of surface tension, there will be a tendency to curve the interface, as a consequence of which there must be a pressure difference across the surface with the highest pressure on the concave side. The expression relating this pressure difference to the curvature of the surface is usually referred to as the Young-Laplace equation. It was published by Young in 1805 and, independently, by Laplace in 1806. From a calculation of the p-V work required to expand the curved surface and so change its surface area, it is relatively straightforward to show that this equation may be written... 

By the first law, the heat change of a reaction carried out at constant pressure, in a system subject to p — V work alone, is given by... 

In summary, p-V work perturbs the energy levels and heat input perturbs the occupational probabilities of the available equilibrium states. One aspect of the second law identifies /T as a factor that makes the heat function an exact differential via the entropy state function... 

It is important to have an understanding of the magnitude of the effect on the reaction that is produced by changing pressure. If we consider work done by pressure as P—V work that is expressed at constant pressure as PAV, a change in volume of lOcm /mol (0.010 1/mol) by a pressure of 1000 atm would produce... 

Keep in mind that a change in pressure accompHshes P-V work that is very small compared to the effects of changing the temperature for Hquids (see Section 3.6). Consequently, the P-jump technique is normally used to study reactions in gaseous systems. 

Because H is a state function, AH (which equals qp) depends only on the initial and final states of the system, not on how the change occurs. At first glance this statement might seem to contradict our discussion in Section 5.2, in which we said that q is not a state function. There is no contradiction, however, because the relationship between AH and qp has the special limitations that only P-V work is involved and that the pressure is constant. 

Now, if P-V work is the only work that can be done, we can substitute Equation 5.12 into Equation 5.5 to ve... 

A gas is confined to a cylinder under constant atmospheric pressure, as illustrated in Figure 5.4. When the gas undergoes a particular chemical reaction, it absorbs 824 1 of heat liom its surroundings and has 0.65 kj of P-V work done on it by its surroundings. What are the values of AH and AE for this process ... 

If 1 mol of CaC03 forms at 298 K under 1 atm pressure, the reaction performs 2.47 kj of P-V work, pushing back the atmosphere as the gaseous CO2 forms. At the same time, 38.95 kJ of heat is absorbed from the environment. What arc the values of AH and of AE for this reaction ... 

The work involved in the expansion or compression of gases is called pressure-volume work P-V work). When pressure is constant in a process, as in our preceding example, the sign and magnitude of the pressure-volume work are given by... 

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