A liter of air, initially at room temperature and atmospheric pressure, is heated at constant pressure until it doubles in volume. Calculate the increase in its entropy during this process.

Short Answer

Expert verified

The increase in entropy is816.51JK-1.

Step by step solution

01

Given Information

Pressure =P=101325Pa

Temperature =T=300K

Volume =V=1L

Heat capacity at constant pressure=Cp=29JK-1

02

Calculation

For an ideal gas, as the volume doubles, the temperature must also double.

The change in entropy is given as:

ΔS=TiTfQTΔS=TiTfCpdTTΔS=Cpln[T]TiTfΔS=CplnTfTiΔS=Cpln2TiTiΔS=Cpln2

For the number of molecules in one liter of air,

n=PVRTn=101325×18.314×300n=40.62mol

Hence, change in entropy for one liter of air can be calculated as:

ΔS=nCpln2ΔS=40.62×29×ln2ΔS=816.51JK-1

03

Final answer

Hence, the entropy of air will be 816.51JK-1when air is heated at constant pressure and its volume doubles.

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Most popular questions from this chapter

A bit of computer memory is some physical object that can be in two different states, often interpreted as 0 and 1. A byte is eight bits, a kilobyte is 1024=210bytes, a megabyte is 1024 kilobytes, and a gigabyte is 1024 megabytes.

(a) Suppose that your computer erases or overwrites one gigabyte of memory, keeping no record of the information that was stored. Explain why this process must create a certain minimum amount of entropy, and calculate how much.

(b) If this entropy is dumped into an environment at room temperature, how much heat must come along with it? Is this amount of heat significant?

An ice cube (mass 30g)0°Cis left sitting on the kitchen table, where it gradually melts. The temperature in the kitchen is 25°C.

(a) Calculate the change in the entropy of the ice cube as it melts into water at 0°C. (Don't worry about the fact that the volume changes somewhat.)

(b) Calculate the change in the entropy of the water (from the melted ice) as its temperature rises from 0°Cto 25°C.

(c) Calculate the change in the entropy of the kitchen as it gives up heat to the melting ice/water.

(d) Calculate the net change in the entropy of the universe during this process. Is the net change positive, negative, or zero? Is this what you would expect?

Use the thermodynamic identity to derive the heat capacity formula

CV=TSTV

which is occasionally more convenient than the more familiar expression in terms of U. Then derive a similar formula for CP, by first writing dHin terms of dSand dP.

In Problem 2.32you computed the entropy of an ideal monatomic gas that lives in a two-dimensional universe. Take partial derivatives with respect to U,A, and N to determine the temperature, pressure, and chemical potential of this gas. (In two dimensions, pressure is defined as force per unit length.) Simplify your results as much as possible, and explain whether they make sense.

Consider an Einstein solid for which both N and q are much greater than 1. Think of each oscillator as a separate "particle."

(a) Show that the chemical potential is

role="math" localid="1646995468663" μ=-kTlnN+qN

(b) Discuss this result in the limits Nqand Nq, concentrating on the question of how much Sincreases when another particle carrying no energy is added to the system. Does the formula make intuitive sense?

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