Learning Materials
Features
Discover
Chapter 5: Q. 5.79 (page 208)
Most pasta recipes instruct you to add a teaspoon of salt to a pot
of boiling water. Does this have a significant effect on the boiling temperature?
Justify your answer with a rough numerical estimate.
There is hardly any effect on the boiling temperature of water.
Over 30 million students worldwide already upgrade their learning with Vaia!
All the tools & learning materials you need for study success - in one app.
Get started for free
Graphite is more compressible than diamond.
(a) Taking compressibilities into account, would you expect the transition from graphite to diamond to occur at higher or lower pressure than that predicted in the text?
(b) The isothermal compressibility of graphite is about 3 x 10-6 bar-1, while that of diamond is more than ten times less and hence negligible in comparison. (Isothermal compressibility is the fractional reduction in volume per unit increase in pressure, as defined in Problem 1.46.) Use this information to make a revised estimate of the pressure at which diamond becomes more stable than graphite (at room temperature).
In Problems 3.30 and 3.31 you calculated the entropies of diamond and graphite at 500 K. Use these values to predict the slope of the graphite- diamond phase boundary at 500 K, and compare to Figure 5.17. Why is the slope almost constant at still higher temperatures? Why is the slope zero at T = 0?
Suppose that a hydrogen fuel cell, as described in the text, is to be operated at and 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, . Let us take for both to be zero at , so that G for a mole of is at .
(a) Using these conventions, estimate the Gibbs free energy of a mole of at . Repeat for .
(b) Using the results of part (a), calculate the maximum electrical work done by the cell at , for one mole of hydrogen fuel. Compare to the ideal performance of the cell at.
Check that equations 5.69 and 5.70 satisfy the identity (equation 5.37)
Below 0.3 K the slope of the °He solid-liquid phase boundary is negative (see Figure 5.13).
(a) Which phase, solid or liquid, is more dense? Which phase has more entropy (per mole)? Explain your reasoning carefully.
(b) Use the third law of thermodynamics to argue that the slope of the phase boundary must go to zero at T = 0. (Note that the *He solid-liquid phase boundary is essentially horizontal below 1 K.)
(c) Suppose that you compress liquid *He adiabatically until it becomes a solid. If the temperature just before the phase change is 0.1 K, will the temperature after the phase change be higher or lower? Explain your reasoning carefully.
What do you think about this solution?
We value your feedback to improve our textbook solutions.
Explanations 
Textbooks 
Exams 
GCSE 
IGCSE 
AS 
A Level 
International A Level 
University Admissions Tests 
Flashcards 
Vaia AI 
Notes 
Study Plans 
Study Sets 
Find a job 
Find a degree 
Student Deals 
Magazine 
Mobile App