CHBE 244: Chemical Engg. Thermodynamics I

Jan 2014

Quiz 1Name:

Part I. (14 points) There are two types of questions in this section: (i) For true or falsequestions, simply write “TRUE” or “FALSE” in the blank space. (ii) For multiple choicequestions circle the correct answer. There is only one correct answer. Full credit will onlybe given for legible answers. No credit will be given if more than one answer is chosen.The order of questions/choices is unique to your exam.

8 pts

1. State whether the following statements are TRUE or FALSE.

(a) All natural processes are reversible.(1 pt)

(b) Irreversible processes are often characterized by friction and dissipative forces.(1 pt)

(c) The efficiency of an irreversible heat engine is given by TH−TCTH

. (1 pt)

(d) Change in entropy of a reversible process is always zero. (1 pt)

(e) Entropy change in an irreversible process is given by dS = δQirrev

T. (1 pt)

(f) Reversible processes are the most efficient. (1 pt)

(g) Microscopic entropy is a relative property that depends on the reference stateentropy. (1 pt)

(h) Entropy is minimum at equilibrium. (1 pt)

6 pts

2. Answer the following multiple choice questions. Only one choice is correct.

(a) (3 pts) A 200 ◦C heat reservoir gains 600 kJ of heat during a process. Its change inentropy is nearest to:

(A) 1.27 kJ/K.

(B) 0.863 kJ/K.

(C) 1.02 kJ/K.

(D) 1.59 kJ/K.

(b) (3 pts) An ideal gas heat engine operating between TH = 200 ◦C and TC = 20 ◦Crejects 50 kJ (i.e., QC = 50 kJ). Estimate the energy required to operate the engine.

(A) 470 J .

(B) 250 J .

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(C) 510 J .

(D) 320 J .

Part II. (24 points) Clearly show all steps involved. Illegible answers may not receive fullcredit.

7 pts

1. Ten kilograms of air (assume ideal gas properties) at 600 kPa and 40 ◦C are heated in arigid container to 250◦C. Assuming that Cp = 1.004 kJ/(kg.K), Cv = 0.717 kJ/(kg.K)and R = 0.287 kJ/(kg.K), calculate

(i) the heat transferred. (3 pts)

(ii) the change in entropy for this process. (4 pts)

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5 pts

2. Air in a 2m3 rigid container cools from 200 ◦C and 400 kPa to 100 ◦C. The surroundingsare at 20 ◦C. Determine the entropy change of the universe.

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3 pts

3. An inventor claims to have developed an automobile engine that burns biofuels at315.5 ◦C with an engine efficiency of 50 %. If the atmospheric air is at 15.5 ◦C, canthis claim be believed?

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5 pts

4. An ideal heat engine (Carnot engine) receives 600 kJ of heat from a heat source at600 ◦C. It rejects 300 kJ of heat to an environment at 10 ◦C. Calculate

(i) the work done by the heat engine (2 pts)

(ii) the maximum possible engine efficiency (2 pts)

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4 pts

5. Bonus Rolling two dice (six-sided cubes with numbers between 1 and 6 on each side)is like putting two particles in six boxes. Compute ∆S for going from double sixes to afour and three.