States of Matter Solid, Liquid and Gas MCQ Questions & Answers in Physical Chemistry | Chemistry

A gas ceases to exist at absolute zero. It is the lowest temperature which can be attained, where volume becomes zero.

Most probable velocity, $${U_{mp}} = \sqrt {\frac{{2\,RT}}{M}} $$
Mean velocity, $${U_{av}} = \sqrt {\frac{{8RT}}{{\pi M}}} $$
Root mean square velocity, $${U_{rms}} = \sqrt {\frac{{3RT}}{M}} $$
$$\eqalign{ & {\text{so}},\,{U_{mp}}:{U_{av}}:{U_{rms}} = \sqrt {\frac{{2RT}}{M}} :\sqrt {\frac{{8RT}}{{\pi M}}} :\sqrt {\frac{{3RT}}{M}} \cr & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = \sqrt 2 :\sqrt {\frac{8}{\pi }} :\sqrt 3 \cr} $$

$$\eqalign{ & d = \frac{{PM}}{{RT}}\,\,{\text{or}}\,\,d \propto \frac{P}{T} \cr & \frac{{{d_1}}}{{{d_2}}} = \frac{{{P_1}}}{{{P_2}}} \times \frac{{{T_2}}}{{{T_1}}}\,\,{\text{or}}\,\,{d_2} = \frac{{{d_1} \times {P_2} \times {T_1}}}{{{P_1} \times {T_2}}} \cr & {d_2} = \frac{{5.46 \times 1 \times 300}}{{2 \times 273}} = 3.0\,\,g\,\,d{m^{ - 3}} \cr} $$

$$\eqalign{ & \frac{{K.E{\text{ of neon at }}{{40}^ \circ }C}}{{K.E{\text{ of neon at }}{{20}^ \circ }C}} \cr & = \frac{{\frac{3}{2}K \times 313}}{{\frac{3}{2}K \times 293}} \cr & = \frac{{313}}{{293}} \cr} $$

$$\eqalign{ & {\text{According to Bragg}}'{\text{s}}\,\,{\text{equation,}} \cr & n\lambda = 2\,d\,{\text{sin}}\theta \cr & \,\,\,n = 2\, \cr & \,\,\,\lambda = 1 \cr & {\text{deflected angle}}\,\theta = {60^ \circ } \cr & d = ? \cr & {\text{Distance between two plane of crystal}}{\text{.}} \cr & 2 \times 1 = 2 \times d \times \sin {60^ \circ } \cr & 2 \times 1 = 2 \times d \times \frac{{\sqrt 3 }}{2} \cr & d = \frac{2}{{\sqrt 3 }} \cr & \,\,\,\,\, = \frac{2}{{1.7}} \cr & \,\,\,\,\, = 1.17\mathop {\text{A}}\limits^{\text{o}} \cr} $$

Gases can be liquefied at low temperature and high pressure.

TIPS/Formulae:
Use Grahams' law of diffusion
$$\frac{{{r_{He}}}}{{{r_{C{H_4}}}}} = \sqrt {\frac{{{M_{C{H_4}}}}}{{{M_{He}}}}} = \sqrt {\frac{{16}}{4}} = 2$$

The fraction of unoccupied site in sodium chloride crystal
$$\eqalign{ & = \frac{{X{\text{ - ray density}} - {\text{pyknometric density }}}}{{X{\text{ - ray density}}}} \cr & = \frac{{2.178 \times {{10}^3} - 2.165 \times {{10}^3}}}{{2.178 \times {{10}^3}}} \cr & = \frac{{0.013 \times {{10}^3}}}{{2.178 \times {{10}^3}}} \cr & = \frac{{13}}{{2178}} \cr & = 5.96 \times {10^{ - 3}}. \cr} $$

The extent to which a real gas deviates from ideal behaviour can be understood by a quantity $$'Z’$$ called the compressibility factor. Easily liquifiable gases like $$N{H_3},S{O_2}$$   etc. exhibit maximum deviation from ideal gas as for them $$Z < \, < \, < 1.$$
$$C{H_4}$$  also exhibits deviation but it is less as compared to $$N{H_3}.$$

$$\eqalign{ & {\text{From the ideal gas equation :}} \cr & PV = nRT \cr & {\text{or}}\,\,n = \frac{{PV}}{{RT}} \cr & \,\,\,\,\,\,\,\,\,\,\,\, = \frac{{3170 \times {{10}^{ - 3}}}}{{8.314 \times 300}} \cr & \,\,\,\,\,\,\,\,\,\,\,\, = 1.27 \times {10^{ - 3}} \cr} $$