(a) State two differences between boiling and evaporation.
(b) A closed inexpansibie vessel contains air saturated with water vapour at 77°C. The total pressure in the vessel is 1007 mmHg. Calculate the new pressure in the vessel if the temperature is reduced 1.2 27°C. [ The s.v.p. of water at 77°C and 27°C respectively are 314 mmHg and 27 mmHg. Treat the air in the vessel as an ideal gas]
(c) The lengtn of a zinc rod at 23°C is 200 m. Calculate the increase in length of the rod when its temperature rises to 33°C. [ expansivity of zinc = 2.6 x 10\(^{-5}\) K\(^{-1}\)]
(d) Explain with there is no temperature change when a solid being heated changes into liquid at its melting point.
Explanation
a)
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Boiling |
Evaporation |
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Takes place at a particular temperature Takes place through-out the whole volume of the liquid. Takes place at a steady temperature |
Takes place at all temperatures Takes place only on the surface of the liquid. Can take place at reduced temperature.
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(b) \(P_1 = 1007 - 314 = 693 mmH_g\)
\(\frac{P_1}{T_1} - \frac{P_2}{T_2} = \frac{693}{350} = \frac{P_2}{300}\)
\(p_2 = \frac{963}{350} \times \frac{300}{1}\) = 594 mmH\(_g\)
Pressure in vessel at 27°C = pressure of air + S.V.P of water at 27°C
= 594 + 27 = 621mm Hg
(c) \(\alpha = \frac{L_2 - L_1}{L_1(\theta_1 - \theta_2)}\)
= 2.6 x 10-5 x 200 (33-23) = 0.052m
(d) At the solid state the molecules are tightly bounded, therefore at the melting point the heat supplied is absorbed and used to break the bonds holding the molecules together.