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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

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Prove that the entropy of mixing of an ideal mixture has an infinite slope, when plotted vs. x, at x = 0 and x= 1.

Suppose that a hydrogen fuel cell, as described in the text, is to be operated at 75°Cand atmospheric pressure. We wish to estimate the maximum electrical work done by the cell, using only the room temperature data at the back of this book. It is convenient to first establish a zero-point for each of the three substances, H2,O2,andH2O. Let us take Gfor both H2andO2to be zero at 25°C, so that G for a mole of H2Ois -237KJat 25°C.

(a) Using these conventions, estimate the Gibbs free energy of a mole of H2at 75°C. Repeat for O2andH2O.

(b) Using the results of part (a), calculate the maximum electrical work done by the cell at 75°C, for one mole of hydrogen fuel. Compare to the ideal performance of the cell at25°C.

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