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Suppose you have a mole of water at 25°Cand atmospheric pressure. Use the data at the back of this book to determine what happens to its Gibbs free energy if you raise the temperature to30°C. To compensate for this change, you could increase the pressure on the water. How much pressure would be required?

Short Answer

Expert verified

So, to bring out the required Gibb's free energy, increase the pressure by 194atm.

Step by step solution

01

Explanation

The initial temperature of the water =25°Cor (273+25)K

The final temperature of the water=30°Cor (273+30)K

Formula Used:

Gibb's free energy expression is

ΔG=-SΔT+VΔP+μΔPP

02

Calculation

The entropy of the water at atmospheric pressure is S=69.91J/K.

Here, volume and pressure are constants.

Hence, the change in pressure is ΔP=0

The change in volume is ΔV=0

So, the equation ΔG=-SΔT+VΔP+μAPbecomes:

ΔG=SΔT+V(0)+μ(0)=SΔT

Substitute

69.91J/Kfor S

5Kfor ΔT

Molar mass of a water molecule is 18g/moland one mole of water molecule is 18g/molx1mol=18gThe Density of the water is 1000kg/m3

Hence, the volume of the water molecule will be:

V=18r110k,/m2×Hin2kmlg=18×10-6m3

Consider the pressure is increased and the Gibbs free energy remains constant

Change in Gibbs free energy ΔG=0

If the change in pressure is ΔP

So, to bring out the required Gibb's free energy, increase the pressure by 194atm.

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Most popular questions from this chapter

Suppose you need a tank of oxygen that is 95% pure. Describe a process by which you could obtain such a gas, starting with air.

Write down the equilibrium condition for each of the following reactions:

(a)2H↔H2(b)2CO+O2↔2CO2(c)CH4+2O2↔2H2O+CO2(d)H2SO4↔2H++SO42-(e)2p+2n↔He4

Sketch a qualitatively accurate graph of G vs. T for a pure substance as it changes from solid to liquid to gas at fixed pressure. Think carefully about the slope of the graph. Mark the points of the phase transformations and discuss the features of the graph briefly.

Repeat the previous problem for the opposite case where the liquid has a substantial negative mixing energy, so that its free energy curve dips |below the gas's free energy curve at a temperature higher than TB. Construct the phase diagram and show that this system also has an azeotrope.

Problem 5.35. The Clausius-Clapeyron relation 5.47 is a differential equation that can, in principle, be solved to find the shape of the entire phase-boundary curve. To solve it, however, you have to know how both L and ∆V depend on temperature and pressure. Often, over a reasonably small section of the curve, you can take L to be constant. Moreover, if one of the phases is a gas, you can usually neglect the volume of the condensed phase and just take ∆V to be the volume of the gas, expressed in terms of temperature and pressure using the ideal gas law. Making all these assumptions, solve the differential equation explicitly to obtain the following formula for the phase boundary curve:

P= (constant) x e-L/RT

This result is called the vapour pressure equation. Caution: Be sure to use this formula only when all the assumptions just listed are valid.

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