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1

### NEET 2013

Maximum deviation from ideal gas is expected from
A
CH4(g)
B
NH3(g)
C
H2(g)
D
N2(g)

## Explanation

The compressibility factor is the term which is measured for a gas to study its deviation from the ideal behaviour. Compressibility factor,

$$Z = {{PV} \over {nRT}}$$

Greater is the difference in the value of Z from 1, greater is the deviation of the gas from ideal behaviour.

Among the given molecules, NH3 is easily liquefiable gas which deviates from ideal behaviour to the maximum extent.
2

### NEET 2013 (Karnataka)

What is the density of N2 gas 227oC and 5.00 atm. pressure? (R = 0.082 L atm K$$-$$1 mol$$-$$1)
A
1.40 g/mL
B
2.81 g/mL
C
3.41 g/mL
D
0.29 g/mL

## Explanation

PV = nRT

$$\Rightarrow$$ PV = $${W \over M}RT$$

$$\Rightarrow$$ $$P = {W \over M} \times {{RT} \over V}$$

$$\Rightarrow$$$$P = {{dRT} \over M}$$   [Density = $${{Mass} \over {Volume}}$$]

$$\Rightarrow d = {{PM} \over {RT}} = {{5 \times 28} \over {0.0821 \times 500}} = 3.41\,g/ml$$
3

### AIPMT 2012 Mains

Equal volumes of two monoatomic gases, A and B at same temperature and pressure are mixed. The ratio of specific heats (Cp/Cv) of the mixture will be
A
0.83
B
1.50
C
3.3
D
1.67

## Explanation

Cp for monoatomic gas mixture of same volume = $${5 \over 2}R$$

$$\therefore$$ CV = $${3 \over 2}R$$

$$\Rightarrow {{{C_P}} \over {{C_V}}} = {{{5 \over 2}R} \over {{3 \over 2}R}} = {5 \over 3} = 1.67$$
4

### AIPMT 2012 Mains

For real gases van der Waals equation is written as

$$\left( {p + {{a{n^2}} \over {{V^2}}}} \right)$$ (V $$-$$ nb) = n RT
where $$a$$ and $$b$$ are van der Waals constants. Two sets of gases are
(I)  O2, CO2, H2 and He
(II)  CH4. O2 and H2

The gases given in set-I in increasing order of b and gases given in set-II in decreasing order of $$a$$, are arranged below. Select the correct order from the following
A
(I) He < H2 < CO2 < O2   (II) CH4 > H2 > O2
B
(I) O2 < He < H2 < CO2   (II) H2 > O2 > CH4
C
(I) H2 < He < O2 < CO2   (II) CH4 > O2 > H2
D
(I) H2 < O2 < He < CO2   (II) O2 > CH4 > H2

## Explanation

Van der Waal gas constant '$$a$$' represent intermolecular force of attraction of gaseous molecules and Van der Waal gas constant 'b' represent effective size of molecules . Therefore order should be

(I) H2 < He < O2 < CO2   (II) CH4 > O2 > H2

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Class 12