Page 73 - SP015 Past Years PSPM Chapter 6 -14 Ver 2020

PSPM SP015

PSPM JAN 2000/2001 SF015/2 No. 14(b)

13. p (atm)
C
p f

2 A
B
2.0 10.0 V (l)

FIGURE 14.4

FIGURE 14.4 shows an ideal gas which is compressed from a volume of 10.0 l to 2.0 l
at constant pressure of 2.0 atm. Heat is then supplied to the system at constant volume
while pressure and temperature is let to change until the system finally reaches the
initial temperature at C. Calculate
(a) the total work done in the above process. [3 m]
(b) the final value of pressure, p f. [3 m]

PSPM 2001/2002 SF015/2 No. 8

5
3
3
14. An ideal gas expands from volume 50 cm to 60 cm at constant pressure 1.01  10 Pa.
If the gas temperature before expansion is 25 C, determine
(a) the temperature after expansion. [2 m]
(b) the total work done by the gas to expand. [2 m]

PSPM 2001/2002 SF015/2 No. 14(b)

15. One mole of a monoatomic ideal gas is at initial temperature of 650 K, while initial
pressure and initial volume are p o and V o respectively. At the beginning stage, this ideal
gas goes through an isothermal expansion process which causes its volume to become
2V o. Then this gas goes through an isovolumetric process and returns to its initial
pressure. Finally this gas goes through an isobaric process causing it to return to its
initial temperature, pressure, and volume.

(a) Sketch a graph of pressure versus volume for the whole process. [4 m]

(b) By using the first law of thermodynamics, prove that the total heat for the whole
process is
Q = (nRT ln 2 – p oV o)
where n is the number of mole, R is the molar gas constant while T is the absolute
temperature. Calculate the total of heat for the whole process. [8 m]

(c) State whether heat is absorbed or released. [1 m]

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