to state

(1)

1.

A closed systein changed from state

"a"

to state

"b"

via the path

a

+

^c

+

b ,

as shown in Fig. 1.

It was found that 250

J

of heat was transferred from sulroundings to the system and 200 J of work was done by the systein during the changing process.

(a) Please calculate the amount of heat transfer (Q,) as the system changes from state

"b"

to state

"a"

through the path

b

+

d

+

a

as illustrated in Fig. 1. During this changing process, 100 J of work is done by sulroudings. You are also asked to indicate that the heat is absorbed or evolved. (5

%)

(b)

As presented in Fig. 1, the system changes from state

"a"

to state

"b"

and then retuilts to state

"a"

via the path

a

+

c

+

b

+

e

-+

a .

You are asked to calculate the amount of work

interaction

(Wb)

between the system and surroundings, if 100

J

of heat is evolved froill the system to surroundings during tltis cyclic process. Is the work done by the system or surroundings? (5

%)

2. Qualitatively plot a practical Rankine power cycle on a T-S diagram and indicate the coitstraint of each step. (5

%)

3.

For water

(1) +

ethaiiol(2) system, its inolar volume change of mixing (A,,,,,B at 300

K

can be expressed by the following equation:

where

x,

and

^XI

are the mole fractioils of water and ethanol, respectively. At 300 K, the density of pure water is 1.0 glcm3 and that of pure ethanol is 0.78 &m3. Now, we try to prepare 100 c11t3 of water

t

ethanol solution with the inolar ratio of water

:

ethanol

=

1

:

1 at 300 K.

(a) Calculate the density of this aqueous solution. (5

%)

(b) How many grams of water and ethanol are needed, respectively, to prepare the solution? (5

%)

(c) Calculate the partial molar volume of ethanol for this solution. (10

%)

(d) Calculate the partial molar volume of ethanol at infinite dilution. (5

%)

4. Describe briefly the

y-4

inethod for vapor-liquid equilibiium (VLE) calculation. (10

%)

(2)

Part I I . dtr%h% ( 5 0 % )

5.

Microelectronic devices are formed by first forming Si02 on a Si wafer by thermal oxidation and some procedures as illustrated in Fig. 2. The second procedure is followed by coating the Si02 with a photoresist. The pattern of the electronic circuit is then placed on the photoresist and the sample is irradiated with

UV

light. If the photoresist is a positive type, the sections that were irradiated with dissolve in the appropriate solvent, and those sections not irradiated will protect the SiO2 from hither treatment. The wafer is then exposed to strong acids, such as HF, which etch the exposed SiOz. It is extremely important to know the kinetics of the reaction so that the proper depth of the channel can be achieved. The dissolution reaction is

SiO, + 6 H F + H2SiF, + 2 H 2 0

(i) From the following initial rate data, determine the rate law. Also estimate the etching rate at 1

wt0/0

of HF.

(ii)

The etching rate may differ at various temperatures. This means that the reaction rate of a chemical reaction always follows Arrhenius behavior. Please give an example of reaction to show the transition state and the energy barrier of a reaction by

Etching rate (nmtmin) HF (wt Oh)

using potential energy plot

as

a function of reaction coordinate. (15%)

Fig. 2 Semiconductor etching

6. Chemical vapor deposition (CVD) is a technique to deposit thin filnis through chemical reactions of gaseous species on a solid substrate. In order to deposit PbTi03 films on Si wafers, a CVD reaction system was designed which used TEL and TTIP as

60 8

the gaseous sources for Pb and Ti, respectively. Also

^{0 2}

was used as an oxidant. A surface reaction scheme concerning the deposition of PbTi03 is proposed as follows.

200 20

600 3 3

1000 40

1400

48

(3)

T E L a

+ 3 0

^a

+

TTIP(@

1 PbTi03() + 4C2H4(@

+

4C3H6(@

+ 4H2qpl

(3) where

o

designates a surface adsorption site, k and k' are the rate constants for adsorption and desorption, respectively,

k3

is the rate constant for PbTi03 deposition.

The above reaction scheme considers an Eley-Rideal mechanism, i.e., a surface reaction among three species: two adsorbed species, TEL and dissociated oxygen, and one gaseous species TTIP, reacting to form PbTi03 films. Considering that reactions in eqs. (1) and (2) are reversible, please answer the following questions.

(i) According to the Langmuir treatment of adsorption, please write down the rate expression for each step including adsol-ption and desorption using deilotations of

6

(the fraction of surface adsorption site covered by the adsorbed molecules) and P (partial pressure for each species, e.g., PTEL as the partial pressure of TEL,

Pol as the partial pressure of oxygen)

(ii) Please express the conservation equation of surface site.

(iii) Please derive the adsorption isotherms for TEL (BTEL.,

)

and dissociated oxygen

⁽

60,) .

(iv) Please show that the deposition rate is linearly proportional to TTIP partial pressure but nonlinear to TEL and

O2

partial pressures.

(20°/0)

7.

For a reactant

A

proceeding the following parallel reactions:

A -+

D (desired) A

^-+

U (undesired).

The rate expressions for each reaction are

q, =

kocAa' and ru

=

kucAa2, respectively. Please answer the following questions.

(i) What is the total consumptioil rate of

A?

(ii) If the rate selectivity parameter is SDU

= rD /

ru, show the relatioil between

Sw

and the rate laws.

(iii)When a1

^-

a 2 >

0,

then what kind of reactor should be adopted in order to

increase the growth rate of

D?

For the same purpose, is the coilcentratioil of

reactant A should be increased or decreased? Why? (1

5%)