In four experiments, blocks Aand B, starting at different initialtemperatures, were brought together in an insulating box and allowedto reach a common final temperature. The entropy changesfor the blocks in the four experiments had the following values (injoules per Kelvin), but not necessarily in the order given.Determine which values for Ago with which values for B.

Short Answer

Expert verified

The values of A that go with values of B are(8,-8),(5,-5),(3,-3),(9,-2)

Step by step solution

01

The given data

In the given four experiments, blocks A and B brought together in an insulating box to reach a final temperature have four entropy values in each experiment.

02

Understanding the concept of entropy 

This problem is based on the concept of the second law of thermodynamics which is an extended postulate to the concept of entropy. The law states that if a process occurs in a closed system, the entropy of the system increases for irreversible processes and remains constant for reversible processes. It never decreases.

Formula:

The entropy change of the system,ΔS0

03

Calculation of the entropy values that of A and B that go along

As per the given concept and equation (i), the entropy change of the system of two blocks A and B with entropy changes S1and S1can be given as:

ΔS0ΔS1+ΔS20ΔS1-ΔS2

Thus, there must exist either a negative equal entropy value of entropy change of block B or a lower negative value of entropy change of block B for every entropy value of block A.

Thus, the values of A and B that match the condition are(8,-8),(5,-5),(3,-3),(9,-2).

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Most popular questions from this chapter

A Carnot engine absorbs 52 kJas heat and exhausts 36 kJas heat in each cycle. (a) Calculate the engine’s efficiency and (b) Calculate the work done per cycle in kilojoules.

In the first stage of a two-stage Carnot engine, energy is absorbed as heat Q1at temperature T1, work W1is done, and energy is expelled as heat Q2at a lower temperature T2. The second stage absorbs that energy as heat Q2 does workW2, and expels energy as heat Q3at a still lower temperature T3. Prove that the efficiency of the engine is(T1-T3)/T1.

A Carnot engine has an efficiency of 22.0 %It operates between constant-temperature reservoirs differing in temperature by 75.0°. (a) What is the temperature of the lower temperature, and (b) What is the temperature of a higher-temperature reservoir?

An inventor has built an engine X and claims that its efficiency X is greater than the efficiency of an ideal engine operating between the same two temperatures. Suppose you couple engine X to an ideal refrigerator (Fig. 20-34a) and adjust the cycle of engine X so that the work per cycle it provides equals the work per cycle required by the ideal refrigerator. Treat this combination as a single unit and show that if the inventor’s claim were true(ifεx>ε), the combined unit would act as a perfect refrigerator (Fig. 20-34b), transferring energy as heat from the low-temperature reservoir to the high-temperature reservoir without the need for work.

Does the entropy per cycle increase, decrease, or remain the same for (a) a Carnot engine, (b) a real engine, and (c) a perfect engine (which is, of course, impossible to build)?

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