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Chapter 5: Q 5.69 (page 199)

What happens when you spread salt crystals over an icy sidewalk? Why is this procedure rarely used in very cold climates?

Short Answer

Expert verified

The transition temperature between the phases will be lower than, implying that the ice on the street will not freeze until the temperature drops to the new phase temperature.

Step by step solution

01

Given information

Salt crystals are spread over an icy sidewalk.

02

Explanation

We know that water freezes at 0°C, thus sprinkling salt on the icy sidewalk will lower the phase temperature. As a result, the transition temperature between the phases will be lower than 0°C, implying that the ice on the street will not freeze until the temperature drops to the new phase temperature.

This approach will not work in very cold nations since the temperature is below the phase temperature of the water and salt mixture, and the mixture also causes concrete damage, so it is only used in very cold countries on rare occasions.

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Most popular questions from this chapter

In a hydrogen fuel cell, the steps of the chemical reaction are
at-electrode:H2+2OH-⟶2H2O+2e-at+electrode:12O2+H2O+2e-⟶2OH-

Calculate the voltage of the cell. What is the minimum voltage required for electrolysis of water? Explain briefly.

A muscle can be thought of as a fuel cell, producing work from the metabolism of glucose:

C6H12O6+6O2⟶6CO2+6H2O

(a) Use the data at the back of this book to determine the values of ΔHand ΔGfor this reaction, for one mole of glucose. Assume that the reaction takes place at room temperature and atmospheric pressure.

(b) What is maximum amount of work that a muscle can perform , for each mole of glucose consumed, assuming ideal operation?

(c) Still assuming ideal operation, how much heat is absorbed or expelled by the chemicals during the metabolism of a mole of glucose?

(d) Use the concept of entropy to explain why the heat flows in the direction it does?

(e) How would your answers to parts (a) and (b) change, if the operation of the muscle is not ideal?

Problem 5.64. Figure 5.32 shows the phase diagram of plagioclase feldspar, which can be considered a mixture of albite NaAlSi3O8and anorthiteCaAl2Si2O8

a) Suppose you discover a rock in which each plagioclase crystal varies in composition from center to edge, with the centers of the largest crystals composed of 70% anorthite and the outermost parts of all crystals made of essentially pure albite. Explain in some detail how this variation might arise. What was the composition of the liquid magma from which the rock formed?

(b) Suppose you discover another rock body in which the crystals near the top are albite-rich while the crystals near the bottom are anorthite-rich. Explain how this variation might arise.

Check that equations 5.69 and 5.70 satisfy the identityG=NAμA+NBμB (equation 5.37)

Sketch qualitatively accurate graphs of Gvs.Tfor the three phases ofH2O(ice, water, and steam) at atmospheric pressure. Put all three graphs on the same set of axes, and label the temperatures0°Cand 100°C. How would the graphs differ at a pressure of0.001bar?
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