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Fundamentals Of Physics
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Short Answer

A sample of an ideal gas is taken through the cyclic process abca as shown in figure. The scale of the vertical axis is set by pb=7.5kPa and pac=2.5kPa. At point a,T=200K .

aHow many moles of gas are in the sample?

What are:

b.The temperature of gas at point b

c.Temperature of gas at point c

d.The net energy added to the gas as heat during the cycle?

  1. The number of moles of gas present in the sample are 1.5 mol.
  2. The temperature of the gas at point b is .1.8 ×103K
  3. The temperature of the gas at point c is 6.0×102K.
  4. The net energy added to the gas as heat during the cycle is 5.0×103 J.

See the step by step solution

Step by Step Solution

Step 1: Given

Pb=7.5 kPa=7500 PaPac=2.5 kPa=2500 Pa

  1. At point a, T=200 K
  2. At point a, V=1 m3
  3. At point b, V=3 m3

Step 2: Determine the concept

Find the number of moles and the temperature of the gas at points b and c present in the sample using the gas law. Net energy added can be found from the net work done by the gas using the given graph.

Formula is as follow:

pivi=nRTi

Here, p is pressure, v is volume, T is temperature, R is universal gas constant and n is number of moles.

Step 3: (a) Determine the number of moles of gas present in the sample

According to the gas law,

PV=nRTn=PVRT

From the given graph, at point a,

n=2500(1)8.314(200)n=1.5 mol

Hence, the number of moles of gas present in the sample are .1.5 mol

Step 4: (b) Determine the temperature of the gas at point b

By gas law,

PbVbPaVa=TbTa

Tb= PbVbPaVa Ta Tb= 7500(3)2500(1) (200)

Tb=1.8 ×103K

Hence, the temperature of the gas at point b is 1.8 ×103K.

Step 5: (c) Determine the temperature of the gas at point c

Similarly,

Tc= PcVcPaVa Ta Tc= 2500(3)2500(1) (200)

Tc=600=6.0×102K

Hence, the temperature of the gas at point c is 6.0×102K.

Step 6: (d) Determine the net energy added to the gas as heat during the cycle

First law of thermodynamics gives,

E=QW

For isothermal process,

Q=WQ=Area under the curveQ=12(ac)(bc)

Substitute the values as:

Q=12(2)(75002500)

Q=5000=5.0×103 J

Hence, the net energy added to the gas as heat during the cycle is 5.0×103 J.

Therefore, the number of moles of gas present in the sample,temperature at a point, and heat added can be foundusing gas law.

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